Paired box proteins as diagnostic biomarkers for endocervical adenocarcinoma

Abstract

In this editorial, we commented on the article by Akers et al published in the recent issue of the World Journal of Clinical Cases. We focused specifically on the role of the transcription factor paired box protein 8 (PAX8) belonging to the family PAX in the carcinogenesis of a gynecologic tumor, endocervical adenocarcinoma, arising from the tissue of mesonephric origin, and the potential diagnostic value for the same type of neoplasms. The global vaccination program of human papillomavirus (HPV) has dramatically reduced the incidence of cervical cancer, including cases of adenocarcinoma. The type of adenoid epithelial origin has a lower frequency of HPV detection but tends to be more aggressive and fatal. Cases of endocervical adenocarcinoma occurring in females of menopause age have been described in the 2023 volume of the World Journal of Clinical Cases and in our study recently published in Oncol Lett. The histopathological findings and immunohistochemical assays showed that the lesions had glandular morphology, and the specimens in these two reports were immunohistochemically positive for the transcription factor PAX8, albeit that they had opposing expression profiles of tumor suppressor p16 and estrogen receptor and the presence of the HPV genome. The presence of a mucin protein, MUC 5AC, as revealed in both studies suggested target molecules for the diagnosis of mucinous adenoid type of uterine tumor and other histological origins. The clinical outcome was unfavorable due to metastasis and recurrence. This prompted the improvement of the antitumor modality, with the introduction of precise targeting therapy. Mucin has now been reported to be the therapeutic target for adenocarcinomas.

Key Words: Cervical adenocarcinoma, Diagnostic biomarker, Paired box protein 8, Embryogenesis, Transcription factor

Core Tip: Paired box proteins (PAXs) are a family of transcription factors that play an important role in the embryogenesis of different tissues through the regulation of gene expression. PAX 2, 5, and 8 are expressed in the sites of mesonephric tissues, and their deregulation contributes to the genesis of urogenital tumors such as cervical and ovarian cancers. Immunohistochemical staining and in situ hybridization tests revealed that the specimens of endocervical adenocarcinoma were positive for the transcription factor PAX8 and human papillomavirus. It is proposed that combined with mucin of glandular tumor, PAX8 can be used as a diagnostic marker for cervical adenocarcinoma.

INTRODUCTION

In 2023, a report by Akers et al[1] published in the World Journal of Clinical Cases described a case of distant metastasis of cervical adenocarcinoma with alterations in several biomarkers including tumor suppressor p16, estrogen receptor, and transcription factor paired box protein 8 (PAX8). The case was also positive for human papillomavirus (HPV)[1]. We recently reported 2 cases of gastric-type endocervical adenocarcinoma; one of the patients was immunohistochemically positive for PAX8[2]. Because PAX protein expression related to the tissue origin of lesions during embryogenesis and published data on the involvement of PAX proteins in the cancers of the ovary and uterine cervix, we aimed to dissect the possible significance of using PAX proteins, especially PAX8, as diagnostic and therapeutic targets of cervical adenocarcinoma.

Role of PAX proteins in mesonephric embryogenesis and carcinogenesis

Gynecologic tumors such as ovarian and cervical cancers arise from the tissues of mesonephric origin during embryogenesis. The transcription factors regulate embryonic development and play a role in organogenesis. The aberrant expression is responsible for the genesis of malignancies. Some members of the PAX family are implicated in these processes.

The PAX family comprises nine members, namely PAX1-9. They are divided into four groups based on their distinct molecular motif composition. The transcription factors are preferentially expressed in different anatomic sites during human embryogenesis to regulate gene expression; in relation to this, the PAX protein family molecules also contribute to carcinogenesis in specific parts of the body.

The members of the PAX family preferentially contribute to the regulation of gene expression of different organs; early expression of PAX2 is essential for the formation of the mesonephric duct[3]. It also compensates for the reduced expression of PAX8 throughout kidney development; the expression of PAX8 is activated in kidney and thyroid tissue during their organogenesis process[4]. In addition, PAX1 and PAX9 are implicated in the development of the skeleton. PAX2, 3, 5, 6, 7, and 8 are implicated in the development of the central nervous system[5], and aberrant expression of these PAX family members contributes to malignancies of the kidneys, thyroid gland, ovary, fallopian tube, and uterine cervix[6-8]. Table 1 summarizes the biological classification and activities of PAX family proteins including their role in tumorigenicity.

Table 1 Classification, embryogenesis, and tumorigenicity of paired box protein family proteins.

Group in PAX family	Member in PAX family	Expression site during embryogenesis	Involvement in tumorigenicity
I	PAX1	Skeleton, thymus, pharyngeal pouch
	PAX9	Skeleton, teeth, thymus
	PAX2	Kidney, CNS	Bladder and renal cancers
II	PAX5	B cells, CNS	Lymphomas
	PAX8	Kidneys, thyroid gland, CNS	Thyroid, ovarian, and cervical cancers
III	PAX3	Neural crest, CNS, muscle	Melanoma, rhabdomyosarcoma
	PAX7	Same as above	Rhabdomyosarcoma
IV	PAX4	Pancreas, gut
	PAX5	Pancreas, gut, and eyes	Gastrointestinal cancers

CNS: Central nervous system; PAX: Paired box protein.

Role of PAX proteins in the genesis of cervical adenocarcinoma

Two major types of tumors, squamous carcinoma and adenocarcinoma[9,10], arise in the epithelial lining of the uterine cervix. Cervical cancer predominantly of squamous epithelial origin is associated with infection of high-risk HPV like types 16 and 18. The high incidence of HPV infection in cell cervical carcinoma offers an opportunity for global eradication through HPV vaccination[11]. Cervical adenocarcinomas, however, form a spectrum from well-differentiated adenoma malignum (a mucinous variant of minimal deviation adenocarcinoma) to poorly differentiated, invasive gastric-type adenocarcinoma[12,13]. Endocervical carcinoma, specifically gastric-type cervical adenocarcinoma, has a low incidence of HPV infection.

Generally, adenocarcinoma of the cervix has a poor prognosis. Regarding distant metastasis, cervical cancer typically metastasizes to local structures through direct invasion, hematogenous dissemination, or dissemination through the lymphatic system[14,15]. It was reported that breast metastases of cervical cancer occurred in the case of high-grade adenocarcinoma with mucinous features that we discussed in our case study[2].

In situ hybridization test revealed that the case of cervical adenocarcinoma was positive for HPV and the transcription factor PAX8. Similarly, we reported 2 cases of gastric-type endocervical adenocarcinoma with one case being positive for PAX8[2]. Our cases presented as lesions of glandular appearance, and microscopically the tumor cells presented as cells of adenoid epithelium (Figure 1). In addition to PAX8 they were positive for a mucin protein, MUC 5AC (Figure 2), and negative for HPV. Furthermore, in contrast to the present report, our cases were negative for both estrogen receptor and the tumor suppressor p16.

Figure 1 Histopathologic presentation of endocervical adenocarcinoma. Representative microscopic images of 2 cases of gastric-type endocervical adenocarcinoma. A: Case 1; B: Case 2. The scale bar is a length of 100 μm.

Figure 2 Immunohistochemical staining of gastric endocervical adenocarcinoma. A: Positive staining for a mucin protein, MUC 5AC, which is a biomarker of mucinous glandular tumor of the uterine cervix; B: Positive staining for the transcription factor paired box protein 8. The scale bar represents a length of 100 μm.

Both PAX2 and PAX8 play an important role in the genesis of the anatomic structure of the ovary, uterus cervix, and uterus corpus during embryonic development. It has been shown that PAX8 is expressed in tumors of the thyroid gland, kidneys, and Müllerian tube, such as malignancies of ovary and endometrium, and its incidence of detection is high in ovarian cancer[16-20]. The possible involvement of PAX8 has been revealed in the genesis of cervical cancer[21,22].

PAX 8 has been recognized as a DNA binding transcription factor. A binding site for it has been identified in the promoter region in Wilms’ tumor gene (WT1), coding for a product for the development of kidney and gonadal glands. The data suggested that part of its role in kidney development was as a modulator of WT1 expression in the kidney[23]. It remains to be tested whether tumors of the cervix and ovary have altered expression of WT1. While high PAX8 level is present in thyroid cancers, it has been reported that the coding region of PAX8 is mutated in patients of thyroid dysgenesis, and it is responsible for elevated thyroid-stimulating hormone levels in congenital hypothyroidism[24]. Given this, the molecules of particular members of the PAX family are proposed to be indicators or biomarkers for the diagnosis of cervical adenocarcinoma or cancer of the cervix in general.

The expression of PAX8 has been noted in tumors of thyroid, renal, and Müllerian tube origins, like neoplasms originating from ovary and endometrium. Meanwhile, however, PAX8 was reported to be expressed in all 20 cases (100%) of benign endocervical epithelium specimens. Additionally, it was expressed in 97%-100% of adenocarcinoma in situ and in 0%-87% of endocervical adenocarcinoma specimens[25,26]. These findings suggest that the incidence of PAX proteins is low with the progression of the tumor and that the aberrant expression profile of tissue antigen due to the differentiation status in malignancy may account for negative PAX8 expression in 1 of our reported cases. The study of numerous clinical samples is needed to clarify this issue.

CONCLUSION

Multiple drivers of cancer involve the genesis of cervical cancer. We immunohistochemically detected the presence of mutant p53 in our reports. However, the oncogenicity-related changes could be highly heterogeneous; our study revealed the absence of mutant k-ras as assayed using a PCR-based amplification refractory mutant system[2]. Our early work showed that in HPV-positive cervical cancer cases, oncogene c-myc was overexpressed due to exon alteration[27] and the change in c-myc, which cooperates with mutant k-ras, results in malignancy, as reported in another study[28]. The gain-of-function mutations of oncogenes together with the mutation of tumor suppressor genes are common changes in malignancies but less specific to particular neoplasms of certain histologic origins. It is therefore proposed that molecules implicated in organogenesis related to tumors can be used as therapeutic targets for adenocarcinomas. The PAX family proteins may fulfill such demands[29,30].