Predictive value of serum calcium ion level in patients with colorectal cancer: A retrospective cohort study

Abstract

BACKGROUND

Serum calcium ion (Ca²⁺) is an economical and readily available indicator as a routine screening test for hospitalized patients. There are no studies related to serum Ca²⁺ level and digestive tract malignancy.

AIM

To evaluate the effectiveness of serum Ca²⁺ level in predicting the prognosis of patients with colorectal cancer (CRC).

METHODS

We retrospectively collected the data of 280 patients diagnosed with CRC who underwent radical surgery at the Affiliated Cancer Hospital of Xinjiang Medical University. By analyzing the clinicopathological features, differences between serum Ca²⁺ concentrations on the first day after surgery were determined. We used the receiver operating characteristic curve to assess the predictive ability of serum Ca²⁺ for survival. Survival analyses were performed using the Kaplan-Meier method, and multivariate Cox proportional risk regression was used to determine association between calibration serum Ca²⁺ levels and CRC survival outcomes.

RESULTS

By receiver operating characteristic curve analysis, the ideal threshold value for Ca²⁺ the first postoperative day and delta serum calcium (δCa²⁺) value were 1.975 and 0.245, respectively. Overall survival (OS) and progression-free survival (PFS) were better in both the high Ca²⁺ group and high δCa²⁺ group on the first postoperative day. The variables identified through univariate analysis were incorporated into multivariate analysis and showed that tumor differentiation (P = 0.047), T stage (P = 0.019), N stage (P < 0.001), nerve vascular invasion (P = 0.037), carcinoembryonic antigen (P = 0.039), baseline serum Ca²⁺ level (P = 0.011), and serum Ca²⁺ level on the first day (P = 0.006) were independent predictors of prognosis for patients undergoing feasible radical CRC surgery. Using the findings from the multifactorial analysis, we developed a nomogram and the calibration showed a good predictive ability.

CONCLUSION

Low serum Ca²⁺ level on the first postoperative day is an independent risk factor for OS and PFS in CRC.

Key Words: Serum calcium ion; Colorectal cancer; Prognosis; Nomogram; Overall survival

Core Tip: Serum calcium ion (Ca²⁺) is a readily available and cost-effective marker used in routine screenings but has not been studied in relation to digestive tract malignancies until now. This study examined the association of serum Ca²⁺ concentrations with clinical indicators in patients with colorectal cancer (CRC) undergoing radical surgery. The results show that reduced serum Ca²⁺ concentrations on the first day after surgery are associated with poorer overall survival and progression-free survival in patients with CRC.

INTRODUCTION

Colorectal cancer (CRC) is one of the malignant tumors with high morbidity and mortality worldwide. According to statistics, CRC ranks third among malignant tumors worldwide, accounting for approximately 10% of all cancer cases[1]. In recent years, with the change of lifestyle and the acceleration of population aging, the incidence and mortality rates of CRC in China have gradually increased. Compared with other regions of the world, the incidence and mortality rates of CRC in China are at an intermediate level[2]. Treatment options for CRC depend on the stage of the disease and the overall health of the patient. Surgical resection is the primary treatment for early-stage CRC, while chemotherapy and radiation may be used in the advanced stages to shrink the tumor and control symptoms[3]. Survival rates for patients with CRC are improving with the development of new treatment options and earlier detection methods. However, the disease remains a significant health burden. If one or a group of clinical test indicators can be found to assist in predicting prognosis, it may prolong the survival time of patients with CRC.

Calcium (Ca²⁺), as one of the most important electrolytes in the body, is a very versatile second messenger that is involved in the regulation of various pathophysiological processes[4]. This includes regulators of cellular activities such as signaling[5], hormone secretion[6], glycogen metabolism[7], and cellular mitosis[8]. Extracellular Ca²⁺ is not only a source of intracellular Ca²⁺ but also plays an important role in the maintenance and stabilization of the cell wall and the formation of blood clots[9]. Most of the current studies on Ca²⁺ and tumors have focused on the effects of intracellular Ca²⁺ on tumorigenesis and development. Less research has been conducted on the relationship between serum Ca²⁺ levels and tumors. However, it has been shown that serum Ca²⁺ levels are associated with clinicopathologic processes such as nutritional status[10], inflammatory response[11], and lipid metabolism[12]. In the colonic environment, dietary Ca²⁺ binds to bile acids, thereby reducing the carcinogenic and pro-tumor effects of bile acids on colonic tissue, while intracellular Ca²⁺, which is mainly derived from circulating Ca²⁺, plays a greater role in inhibiting the proliferation of normal and neoplastic colorectal epithelial cells, promoting differentiation and apoptosis.

Studies have shown that storage-operated Ca²⁺ channel-regulated Ca²⁺ entry is involved in inflammation and CRC progression[13,14]. Recent evidence suggests that intracellular Ca²⁺ remodeling may contribute to cancer hallmarks[15]. Ca²⁺ intake also has beneficial effects on reducing the incidence of CRC and improving survival in several observational studies[16,17]. The findings of a prospective study conducted in Sweden indicated that there was a positive correlation between the concentration of circulating albumin-corrected serum total Ca²⁺ and the risk of CRC[18]. On the contrary, two large European prospective cohort studies indicated that higher levels of serum Ca²⁺ were associated with reduced risk of CRC development[19].

Serum Ca²⁺ is an economical and readily available indicator as a routine screening test for hospitalized patients. There are no studies related to serum Ca²⁺ level and digestive tract malignancy. Based on the above findings, we hypothesize that serum Ca²⁺ level may play a role in predicting the prognosis of patients with CRC.

MATERIALS AND METHODS

Study populations

The present study retrospectively and consecutively collected data on patients with CRC attending Xinjiang Medical University Cancer Hospital (Xinjiang, China) between 2016 and 2018. The inclusion criteria included: (1) Pathologic diagnosis of definite CRC; (2) Patients with radical resection; (3) Complete clinical case data; and (4) Complete follow-up data. The exclusion criteria included: (1) Those with previous or concurrent other primary cancer foci; (2) Those who underwent neoadjuvant radiotherapy or traditional Chinese medicine; (3) Those who have had two or more surgeries; (4) Death caused by non-CRC factors; and (5) Serious diseases that affect blood Ca²⁺ levels (e.g., hypercalcemia, hypocalcemia). Based on the sample size, a total of 280 patients’ medical records were collected.

Data collection

All clinicopathological data were obtained from the Department of Case Management of the Affiliated Cancer Hospital of Xinjiang Medical University. With reference to the relevant high-quality literature research indexes at home and abroad in the past 5 years and combined with the actual situation of our hospital, 15 research indexes were collected[20,21]. Specifically, they included age, sex, ethnicity, body mass index (BMI), tumor growth site, tumor stage, degree of differentiation, microsatellite stability, neural vascular invasion, carcinoembryonic antigen (CEA), baseline carbohydrate antigen 19-9 (CA19-9), baseline serum Ca²⁺ levels, serum Ca²⁺ level on the first postoperative day, and delta serum calcium (δCa²⁺). Baseline indexes were defined as the results of the first laboratory test on admission. The δCa²⁺ value was defined as the absolute value of the baseline serum Ca²⁺ value minus the serum Ca²⁺ value on the first postoperative day.

The primary study endpoint was overall survival (OS), defined as the time from first admission or diagnosis to death or final follow-up. The secondary study endpoint was progression-free survival (PFS), defined as the time from first admission or diagnosis to first progression (including progression events such as local recurrence and distant metastasis). The Ethics Committee of the Affiliated Cancer Hospital of Xinjiang Medical University approved the ethical review after reviewing that the study complied with ethical principles (No. G-2015021). Written informed consent was obtained from all participants. The cutoff for follow-up was observation of the outcome event or 60 months of follow-up. Median follow-up time was 30 months.

Statistical analyses

Depending on the distribution of the data, continuous variables are described as the mean ± SD or median (Q1 to Q3). Categorical variables are expressed as absolute numbers or percentages. For normally distributed data, the independent samples t-test was used for differences between two groups, otherwise the Mann-Whitney U test was used. For comparisons between groups Fisher’s exact test and Pearson’s χ² test were used. The accuracy of baseline serum Ca²⁺ levels, δCa²⁺ values, and serum Ca²⁺ levels on the first postoperative day for prognostic prediction was evaluated by using receiver operating characteristic curve (ROC). The δCa²⁺ value and the serum Ca²⁺ level on the first postoperative day were selected as prognostic indicators based on the area under the ROC curve (AUC). The cut-off value was determined from the Youden index derived from the ROC, and the cut-off value for the δCa²⁺ value was 0.245 and the cut-off value for the serum Ca²⁺ level on the first postoperative day was 1.975. Based on the cut-off value results, the data were categorized into δCa²⁺ high group and low group, and postoperative day 1 serum Ca²⁺ high group and low group, and Kaplan-Meier curves were plotted separately, and the differences were assessed using log-rank test. Independent risk factors for OS and PFS were determined by univariate and multivariate Cox regression analyses. Nomograms of 1-year, 3-year, and 5-year survival of patients with CRC were plotted using the R software package “rms.” Next, internal validation of the nomogram was performed using the bootstrap method. Calibration curves were used to assess the agreement between predicted and observed survival. Decision curve analysis was used to assess the clinical utility of the nomogram. All statistical tests were two-sided and differences were considered statistically significant at P < 0.05. All statistical data were analyzed with SPSS 26.0 (IBM SPSS Statistics, Armonk, NY, United States), GraphPad Prism 10.0 (GraphPad Software, Boston, MA, United States), and R4.2.0. The description of baseline information, Spearman’s rank correlation analysis, and Cox regression analysis were performed using SPSS, and ROC and Kaplan-Meier curves were generated using GraphPad Prism. Noetherian and calibration plots were drawn in R using the rms package. Models were compared using the “survcomp” package. All statistical tests were two-sided and differences were considered statistically significant at P < 0.05.

RESULTS

Patients’ characteristics

In this study, clinical data of 280 patients were collected by combining inclusion and exclusion criteria. They were categorized into 179 patients in the high-level group and 101 patients in the low-level group based on the critical value of serum Ca²⁺ on the first postoperative day. In comparing the baseline data, there were significant differences between the two groups in terms of age (P = 0.012), degree of tumor differentiation (P = 0.018), CEA (P = 0.002), Ca²⁺-baseline (mmol/L) (P = 0.005), and δCa²⁺ value (P < 0.001) (Table 1). There were no significant differences between race and sex groups.

Table 1 Baseline data of 280 patients with colorectal cancer, n (%).

Characteristics		Ca2+-first postoperative day		P value
		High group (> 1.975 mmol/L)	Low group (< 1.975 mmol/L)
n		179	101
Ethnic group				0.821
	Han ethnic group	149 (83.2)	83 (82.2)
	Others	30 (16.8)	18 (17.8)
Sex				0.693
	Female	77 (43.0)	41 (40.6)
	Male	102 (57.0)	60 (69.4)
Age (years)				0.012a
	< 65	121 (67.6)	53 (52.5)
	≥ 65	58 (32.4)	48 (47.5)
BMI				0.383
	< 23.5	65 (36.3)	42 (41.6)
	≥ 23.5	114 (63.7)	59 (58.4)
Tumor location				0.709
	Right half of colon	37 (22.6)	19 (15.1)
	Left half of colon	142 (77.4)	82 (84.9)
Degree of differentiation				0.018a
	High differentiation	24 (13.4)	3 (3.0)
	Moderately differentiated	127 (70.9)	80 (79.2)
	Poorly differentiated	28 (15.6)	18 (17.8)
T stage				0.313
	T1-2	39 (21.8)	21 (20.8)
	T3	106 (59.2)	53 (52.5)
	T4	34 (19.0)	27 (26.7)
N stage				0.907
	0	102 (54.7)	55 (52.3)
	N1	48 (45.3)	28 (47.7)
	N2	29 (16.2)	18 (17.8)
Neurovascular invasion				0.463
	No	133 (74.3)	79 (78.2)
	Yes	46 (25.7)	22 (21.8)
MSI				0.698
	MSS	164 (91.6)	94 (93.1)
	MSI-H	15 (8.4)	7 (6.9)
CEA (ug/L)				0.002a
	< 5	129 (72.1)	54 (53.5)
	≥ 5	50 (27.9)	47 (46.5)
CA19-9 (U/mL)				0.304
	< 39	158 (85.8)	90 (90.7)
	≥ 39	21 (14.2)	11 (9.3)
Hb (g/L)				0.753
	< 120	50 (27.9)	30 (29.7)
	≥ 120	129 (72.1)	71 (70.3)
PLT (109/L)				0.641
	< 330	143 (79.9)	83 (82.2)
	≥ 330	36 (20.1)	18 (17.8)
Alb (g/L)				0.175
	< 40	65 (36.3)	45 (44.6)
	≥ 40	114 (63.7)	56 (55.4)
Ca2+-baseline (mmol/L)				0.005a
	< 2.11	24 (7.5)	11 (9.3)
	≥ 2.11	155 (92.5)	90 (90.7)
δCa2+				< 0.001a
	< 0.245	145 (81.0)	28 (27.7)
	≥ 0.245	34 (19.0)	73 (72.3)

^aP < 0.05.

δCa²⁺: Delta serum calcium value; Alb: Albumin; BMI: Body mass index; CA19-9: Carbohydrate antigen 19-9; Ca²⁺-baseline: Baseline serum calcium ion levels; Ca²⁺-first postoperative day: Serum calcium ion level on the first day of postoperative period; CEA: Carcinoembryonic antigen; Hb: Hemoglobin; MSI: Microsatellite; PLT: Platelet.

Ca²⁺-related indicators predict prognostic value

To assess the predictive value of serum Ca²⁺ levels in patients with CRC, we performed ROC analysis of baseline serum Ca²⁺ levels and δCa²⁺ values. The baseline serum Ca²⁺ level AUC was 0.502, the AUC on the first postoperative day was 0.655 with a critical value of 1.975, and the δCa²⁺ value AUC was 0.625 with a critical value of 0.245 (Figure 1). Restricted cubic spline revealed a nonlinear relationship between Ca²⁺-first postoperative day and hazard ratio (HR) in patients with CRC. The results showed that HR gradually decreased with the increase of Ca²⁺ (Figure 2). This suggests that Ca²⁺-first postoperative day is a patient-protective factor.

Figure 1 Receiver operating characteristic curve of serum calcium ion-related indicators to predict outcome. δCa²⁺: Delta serum calcium; AUC: Area under the receiver operating characteristic curve; Ca²⁺-baseline: Baseline serum calcium ion levels; Ca²⁺-first postoperative day: Serum calcium ion level on the first day of postoperative period.

Figure 2 Restricted cubic spline curves for serum calcium ion level on the first day of the postoperative period in colorectal cancer. Ca²⁺-first postoperative day: Serum calcium ion level on the first day of postoperative period; CI: Confidence interval.

Correlation studies of serum Ca²⁺ levels on the first postoperative day with other studied variables

Spearman’s rank correlation analysis was conducted on age, sex, ethnic group, BMI, CEA, CA19-9, hemoglobin, blood platelet, albumin and serum Ca²⁺ level (high and low group) on the first postoperative day to analyze the variables related to serum Ca²⁺ level on the first postoperative day. Age, ethnic group, CEA, and CA19-9 were inversely associated with serum Ca²⁺ levels on the first postoperative day. Age (P < 0.001) and CEA (P = 0.002) were significant with serum Ca²⁺ levels on the first postoperative day. BMI (P = 0.042) and albumin (P = 0.005) were positively correlated with serum Ca²⁺ levels on the first postoperative day, and the correlation was equally significant (Table 2).

Table 2 Correlation between clinical data variables and serum calcium ion levels on the first postoperative day.

Relevant factor	Spearman’s correlation coefficient	P value
Age (years)	-0.253	< 0.001a
Sex	0.003	0.963
Ethnic group	-0.038	0.600
BMI	0.148	0.042a
CEA	-0.224	0.002a
CA19-9	-0.035	0.673
Hb	0.129	0.075
PLT	0.052	0.476
Alb	0.203	0.005a

^aP < 0.05.

Alb: Albumin; BMI: Body mass index; CA19-9: Carbohydrate antigen 19-9; CEA: Carcinoembryonic antigen; Hb: Hemoglobin; PLT: Platelet.

Survival analyses

Kaplan-Meier analysis was conducted on survival differences between δCa²⁺ groups and high and low serum Ca²⁺ levels on the first postoperative day. We found that the OS time was shorter in the δCa²⁺ high group, with a statistically significant difference between the two groups (log-rank P = 0.0079, HR = 1.954) (Figure 3A). The higher serum Ca²⁺ level was longer in the group, with a statistically significant difference between the two groups (log-rank P = 0.0007, HR = 0.415) (Figure 3B). Similarly, in the PFS analysis, patients in the δCa²⁺-high group had shorter PFS (log-rank P = 0.0007, HR = 2.385) (Figure 3C), and patients with higher serum Ca²⁺ level on the first day after surgery had a longer PFS (log-rank P = 0.0003, HR = 0.3867) (Figure 3D).

Figure 3 Overall survival and progression-free survival stratified by Δ calcium value and serum calcium ion level on the first day of postoperative period. A: Overall survival (OS) stratified by delta serum calcium (δCa²⁺) value (P = 0.0079, hazard ratio [HR] = 1.954); B: OS stratified by serum Ca²⁺ ion level on the first day of postoperative period (Ca²⁺-first postoperative day) (P = 0.0007, HR = 0.415); C: Progression-free survival (PFS) stratified by δCa²⁺ value (P = 0.0007, HR = 2.385); D: PFS stratified by Ca²⁺-first postoperative day (P = 0.0003, HR = 0.3867).

Univariate analysis and multivariate analyses

Univariate analysis using Cox regression analysis showed that tumor differentiation (P < 0.001), T stage (P < 0.001), N stage (P < 0.001), nerve vascular invasion (P < 0.001), CEA (P < 0.001), baseline serum Ca²⁺ (P = 0.042), serum Ca²⁺ on the first postoperative day (P < 0.001), and δCa²⁺ value (P = 0.010) were associated with the prognosis of patients undergoing feasible radical CRC surgery. The variables selected by univariate analysis were included in multivariate analysis, which showed that tumor differentiation (P = 0.047), T stage (P = 0.019), N stage (P < 0.001), nerve vascular invasion (P = 0.037), CEA (P = 0.039), baseline serum Ca²⁺ level (P = 0.011), and serum Ca²⁺ level on the first day (P = 0.006) were independent risk factors affecting the prognosis of patients undergoing feasible radical CRC surgery (Table 3).

Table 3 Univariate and multivariate analyses of clinicopathological data in patients with colorectal cancer.

Characteristics	Univariate analysis, HR (95%CI)	P value	Multivariate analysis, HR (95%CI)	P value
Ethnic group		0.610	-	-
Han ethnic group
Others	0.840 (0.429-1.643)
Sex		0.021a		0.031a
Female
Male	1.848 (1.097-3.115)		1.796 (1.056-3.054)
Age (years)		0.622	-	-
< 65
≥ 65	1.134 (0.688-1.867)
BMI (kg/m2)		0.448	-	-
< 23.5
≥ 23.5	0.830 (0.513-1.343)
Tumor location		0.387	-	-
Right half of colon
Left half of colon	1.330 (0.697-2.535)
Degree of differentiation		< 0.001a		0.047a
High differentiation
Moderately differentiated	3.250 (0.788-13.399)	0.103	2.056 (0.483-8.753)	0.330
Poorly differentiated	8.192 (1.920-34.960)	0.004a	3.717 (0.845-16.348)	0.082
T stage		< 0.001a		0.019a
T1-2
T3	3.272 (1.290-8.303)	0.013a	1.447 (0.518-4.037)	0.481
T4	5.820 (2.220-15.261)	< 0.001a	2.874 (1.034-7.985)	0.043a
N stage		< 0.001a		< 0.001a
0
N1	2.063 (1.150-3.702)	0.015a	1.321 (0.696-2.509)	0.394
N2	4.575 (2.564-8.164)	< 0.001a	3.407 (1.763-6.586)	< 0.001a
Neurovascular invasion		< 0.001a		0.037a
No
Yes	2.576 (1.588-4.178)		1.820 (1.036-3.196)
MSI		0.234
MSS
MSI-H	0.495 (0.156-1.575)
CEA (ng/mL)		< 0.001a		0.039a
< 5
≥ 5	2.398 (1.489-3.863)		1.709 (1.027-2.845)
CA19-9 (U/mL)		0.148
< 39
≥ 39	1.611 (0.844-3.073)
Hb (g/L)		0.389
< 120
≥ 120	0.800 (0.481-1.330)
PLT (109/L)		0.284
< 330
≥ 330	1.358 (0.776-2.379)
Alb (g/L)		0.636
< 40
≥ 40	0.890 (0.549-1.443)
Ca2+-baseline		0.042a		0.011a
< 2.11
≥ 2.11	3.326 (1.045-10.584)		4.762 (1.426-15.905)
Ca2+-first postoperative day		< 0.001a		0.006a
High
Low	2.234 (1.387-3.597)		2.315 (1.276-4.199)
δCa2+		0.010a		0.506
Low
High	1.876 (1.166-3.020)		0.820 (0.458-1.471)

^aP < 0.05.

δCa²⁺: Delta serum calcium; Alb: Albumin; BMI: Body mass index; CA19-9: Carbohydrate antigen 19-9; Ca²⁺-first postoperative day: Serum calcium ion level on the first day of postoperative period; CEA: Carcinoembryonic antigen; CI: Confidence interval; Hb: Hemoglobin; HR: Hazard ratio; MSI: Microsatellite; PLT: Platelet.

Establish and evaluate the prediction model

Based on the results of multivariate analysis, we selected sex, N stage, and serum Ca²⁺ level on the first postoperative day to establish a nomogram to predict the OS of patients undergoing feasible radical CRC surgery (Figure 4). The calibration curves of 1-, 3-, and 5-year OS illustrated good calibration between the predicted and actual survival probabilities in the whole cohort (Figure 5). Additionally, decision curve analysis further confirmed the significant clinical efficacy of this nomogram model in predicting survival probabilities at 1, 3, and 5 years (Figure 6).

Figure 4 Nomograph of the model composed of T stage, N stage, and serum calcium level on the first postoperative day. CaFPD: Calcium level on the first postoperative day.

Figure 5  Calibration curves to predict 1-year, 3-year, and 5-year overall survival.

Figure 6 Decision curve analyses with clinical net benefits of the nomogram at 1 year, 3 years, and 5 years. A: Decision curve analyses with clinical net benefits of the nomogram at 1 year; B: Decision curve analyses with clinical net benefits of the nomogram at 3 years; C: Decision curve analyses with clinical net benefits of the nomogram at 5 years.

DISCUSSION

In this study, through retrospective analysis of the clinical case data of 280 CRC patients in our hospital from 2016 to 2018, we found that the decrease in postoperative Ca²⁺ level and the large fluctuation of preoperative and postoperative Ca²⁺ level were independent risk factors for the prognosis of patients with feasible radical CRC surgery. Meanwhile, a correlation was found between the postoperative Ca²⁺ level and multiple clinical characteristics and blood indicators. The prognostic prediction model with sex, N stage, and serum Ca²⁺ level on the first postoperative day as variables had good predictive value.

Ca²⁺ is one of the essential nutrients in the human body. It exists in the form of Ca²⁺ in the blood, which is the most abundant cation in the human body[22]. In addition to its involvement in bone mineralization[23], it is also essential for maintaining the normal function of nerves[24], muscles[25], and the heart[26]. The main direction of previous Ca²⁺ research is in it as a signaling molecule mediating various physiological mechanisms and participating in various physiopathological activities[27]. Most studies on serum Ca²⁺ concentration and tumors have focused on multiple myeloma and parathyroid tumors[28]. Mainly because the above two tumors themselves can cause changes in the serum Ca²⁺ level, and the serum Ca²⁺ level has been widely recognized as a tumor marker of the above tumors[29]. However, the relationship between serum Ca²⁺ and other malignancies has not been widely verified. This study started from clinical data and found that serum Ca²⁺ levels were associated with the prognosis of patients with CRC. In particular, the postoperative serum Ca²⁺ level is an independent risk factor affecting the prognosis of patients with CRC with feasible radical surgery.

In recent years, it has been reported that aspirin can inhibit the proliferation of CRC cells, mainly relying on the manipulation of Ca²⁺ influx in the Ca²⁺ pool by its main metabolite, salicylate[30]. Aspirin, as an adjuvant drug, can enhance the effects of neoadjuvant chemoradiotherapy and improve the prognosis of patients with rectal cancer. For patients with CRC treated with preoperative neoadjuvant therapy, the combination of aspirin may be considered a better choice[31]. However, as aforementioned, the main direction of these studies is that Ca²⁺ plays a role in tumor proliferation as a signaling molecule in the cell. It has also been reported that increasing Ca²⁺ intake may be associated with prevention of colon adenoma and improving CRC prognosis. This literature also points to the same important role in the development and development of colorectal tumors[32]. This study was only used as a clinical observational study and did not monitor and analyze serum Ca²⁺ levels.

With the improvement of people’s living standards and the increase of obesity, BMI as a risk factor for the development of CRC has been confirmed[33]. Murphy et al[34] found limited evidence of heterogeneity between BMI and CRC risk, suggesting that obesity affects almost all the major pathways involved in colorectal carcinogenesis. However, BMI is not a risk factor for CRC in patients with Lynch syndrome[34]. Our study found a correlation between postoperative Ca²⁺ level and patients’ BMI, which may also be one of the reasons for the correlation between Ca²⁺ level and prognosis. Meanwhile, the involvement of Ca²⁺ in lipid metabolism has been clearly confirmed[12]. On the one hand, Ca²⁺ can activate certain enzymes and promote the decomposition and oxidation of fatty acids, helping to regulate the fat levels in the body. On the other hand, Ca²⁺ also participate in the balance of intestinal microbial flora, and play an important role in maintaining intestinal health. Studies have shown that lipid metabolism disorders can lead to imbalance of intestinal flora and damage of intestinal mucosa, which leads trigger inflammatory response and oxidative stress. These responses can damage intestinal mucosal cells, causing abnormal hyperplasia and mutation, eventually leading to the development of CRC. Moreover, disturbed lipid metabolism can also affect cell signaling and gene expression, further contributing to the development of CRC. Therefore, it is necessary to determine whether the change of Ca²⁺ level reflects lipid metabolism to some extent and further affects the prognosis of CRC.

With the growth of age, the body’s ability to absorb Ca²⁺ gradually decreases, resulting in decreased Ca²⁺ levels in the body[35]. The alteration of free Ca²⁺ concentration in the cytoplasm, in combination with other signal-transduction cascades, regulates a variety of cellular processes through a universal signaling mechanism. The involvement of several protein kinases is responsible for intracellular Ca²⁺ signaling and homeostasis, leading to numerous physiological and pathological consequences, such as cell cycle, proliferation, apoptosis, gene transcription, cell migration arrangement and regulation. It is therefore not surprising that certain Ca²⁺-mediated signaling pathways are implicated in tumorigenesis and progression[36]. The dysregulation of Ca²⁺ is implicated in driving a diverse array of cancer pathways, which may manifest as tissue-specific, context-specific, or universal among different types of cancers. Previously overlooked in the realm of cancer research, the regulation of Ca²⁺ presents a promising avenue for developing future context-specific treatments for various forms of cancer[37]. There are specific differences in pathological characteristics and clinical characteristics between middle-aged and middle-aged patients in patients with CRC. In this study, we conducted statistical analyses of the age of both groups by using the postoperative Ca²⁺ level as the basis for grouping. The results showed a statistically significant difference in age between the two groups. However, due to the small sample size of this study, further stratification analysis was not conducted to clarify the specific correlation with the level of Ca²⁺ in elderly patients and the role of the prognostic impact. In the future, we need to clarify the relationship between the postoperative Ca²⁺ level and the age through more in-depth research to provide a scientific basis for improving the surgical effect of elderly patients.

A key step in cancer progression is metastasis, which is largely driven by an invasive process known as epithelial-mesenchymal transition (EMT). When epithelial cells adopt a mesenchymal cell phenotype, they exhibit changes in anterior-posterior polarity conformation, which enhances migration and invasiveness to increase cancer metastasis. EMT is induced by a variety of growth factors[38]. These include epidermal growth factor, fibroblast growth factor and transforming growth factor beta. Although these growth factors utilize disparate mechanisms to promote EMT, it is notable that the majority of these factors rely on Ca²⁺ signaling to fulfil their biological roles[39]. Ca²⁺ signaling plays a pivotal role in EMT by driving the expression of mesenchymal marker genes and promoting extracellular matrix degradation[37].

Albumin is one of the important nutrients in the blood, which can reflect the nutritional status of the individual. Changes in albumin levels in postoperative patients, which are usually considered important indicators for assessing rehabilitation status and nutritional status. Nutritional status is clearly related to the prognosis of various malignant tumors, especially colorectal malignant tumors as one of the digestive tract tumors, and nutritional status is particularly important in affecting its prognosis. Clinical data from multiple studies show that malnutrition is a risk factor for poor prognosis[40]. In this study, a significant correlation between postoperative Ca²⁺ levels and albumin levels by spearman correlation analysis. This finding reveals us the potential role of Ca²⁺ in the assessment of nutritional status. This correlation may be one of the reasons why postoperative Ca²⁺ affects the prognosis and should be supported by further clinical data.

The fact that Ca²⁺ participate in inflammatory responses through multiple pathways is a widely validated fact[41]. The decrease in Ca²⁺ levels was obvious in patients with heavy inflammatory response. Some studies show that serum Ca²⁺ serves as an important monitoring index of the intensive care department, and its high and low changes are related to the prognosis of severe patients[42]. Studies have shown that the inflammatory response is an independent risk factor for prognosis in patients with CRC, while the inflammatory response affects the response to immunotherapy in some types of patients with CRC. This study found that reduced Ca²⁺ levels in postoperative patients was a prognostic risk factor. It also seems not difficult to understand the results of this study in terms of the level of inflammatory response. However, how serum Ca²⁺ acts on the development of CRC are not clear. Meanwhile, most of the patients in this study received adjuvant chemotherapy after surgery, and whether the serum Ca²⁺ level affected the therapeutic effect of chemotherapy in this part of patients deserves a more in-depth study.

There this study had some limitations. This study was a single-center retrospective cohort study with a small sample size, which does not allow for more stratified analyses to reveal the deeper significance and value of serum Ca²⁺ levels in the development of CRC. Second, studies on Ca²⁺ metabolism and gastrointestinal tumor development must consider not only serum Ca²⁺ levels but also dietary intake and factors regulating Ca²⁺ homeostasis, including serum vitamin D and parathyroid hormone levels. The present study was conducted mainly in a single hospital, with a relatively small sample size and covering only patient populations in a specific region. To improve the breadth of the study and the external validity of the conclusions, a multicenter, large-sample study design should be considered in the future, covering patients from different regions and populations. This will help us better understand the association between chronic diseases and blood Ca²⁺ levels in different regions and pathologic contexts. In the current study, we included hypertension, diabetes mellitus, cardiovascular and cerebrovascular diseases, and chronic obstructive pulmonary disease as overall covariates in the model, but in reality, these chronic diseases may have different subtypes and clinical phenotypes in the clinical setting. For example, patients with hypertension may be grouped into subtypes based on disease duration, control, comorbidities, and so on; patients with diabetes may be further categorized based on glycated hemoglobin levels, insulin use, and so on. Therefore, future studies should consider a more detailed stratified analysis to reveal the different effects of chronic disease subtypes on blood Ca²⁺ levels. Many patients with chronic diseases are often accompanied by multiple medications, and these medications (e.g., antihypertensive agents, hypoglycemic agents, antiplatelet agents) may have direct or indirect effects on blood Ca²⁺ levels, bone metabolism, and cardiovascular function. Future studies could incorporate patients’ medication history to explore the potential relationship between pharmacologic interventions and blood Ca²⁺ levels. This would provide a more precise basis for clinical management, especially in patient populations with multiple co-morbidities. Lifestyle (e.g., diet, exercise, smoking, alcohol consumption) is an important factor influencing chronic disease and health status; however, this paper failed to systematically consider the potential impact of lifestyle on the study findings. Future studies could incorporate lifestyle factors into analytic models to explore how they affect blood Ca²⁺levels and disease management in patients with chronic diseases. In addition, intervention studies (e.g., improved diet, increased exercise) would be useful in assessing the long-term effects of lifestyle changes on chronic diseases and related biomarkers (e.g., blood Ca²⁺).

This study relied primarily on an internal validation set to evaluate the model; however, internal validation alone does not allow for a comprehensive assessment of the applicability and accuracy of the model in different patient populations. To improve the external validation of the model, future studies will introduce independent validation datasets, especially from different regions, different clinical settings or patient populations with different characteristics. This will help to assess the model’s ability to generalize and ensure its stability and accuracy across different populations. In addition to assessing the accuracy of the model through external validation sets, attention should also be paid to the performance of the model in actual clinical applications. For example, clinical trials or prospective studies can be conducted to track the impact of the model on patient management, treatment decisions, and prognosis prediction in the real world. Long-term follow-up data will help assess the continued stability and clinical validity of the model.

However, we can still draw inspiration from this study, especially in clinical work, whether appropriate Ca²⁺ supplementation would improve the prognosis of CRC patients. For cancers of the digestive tract such as CRC, nutrition and inflammation have a great impact on the prognosis of patients. Serum Ca²⁺ reflect the nutritional and inflammatory status of patients, and they are also very easy to obtain in the clinic. We can intervene in advance by preoperative and postoperative Ca²⁺ levels to improve the prognosis of patients. This may provide some guidance in our future clinical patient management. The Ca²⁺ levels in this study were all concentrated around 7-10 days after the patients were first admitted to the hospital, so we were unable to analyze the long-term changes in Ca²⁺ levels and whether long-term changes in Ca²⁺ levels would affect the prognosis of patients with CRC. However, this is one of the questions we would like to address, i.e. whether prognosis can be predicted earlier after a patient’s diagnosis, as is the case with postoperative Ca²⁺ supplementation, thus helping the clinic to implement more aggressive treatments for patients and improve prognosis.

CONCLUSION

In conclusion, our findings suggest that Ca²⁺ on the first postoperative day is an independent prognostic biomarker affecting OS and DFS in patients with CRC. Ca²⁺ on the first postoperative day may be a practical biomarker for prognostic prediction in laryngeal and pharyngeal tumors.