Challenges of deciphering gastric cancer heterogeneity

Table 3 Common protein biomarkers used in clinical settings for gastric cancer management

Biomarker	Name of protein	Clinical application	Related cancer types
CEA	Carcinoembryonic antigen	Used as a diagnostic aid in different cancers, primarily colorectal cancer. Additionally used as an aid for monitoring response to treatment and detecting recurrence of disease	Colorectal, pancreatic, breast, lung, thyroid, ovarian, endometrial, liver, and bladder cancers. Elevated in benign conditions, such as smoking, peptic ulcer disease, inflammatory bowel disease, pancreatitis, hypothyroidism, cirrhosis, biliary obstruction, and bronchitis
CA19-9	Cancer antigen 19-9	Used as an aid for assessing the effectiveness of treatment and for detecting the recurrence of disease	Colorectal, oesophageal, liver, and pancreatic cancers. Elevated levels common in benign conditions, such as pancreatitis, biliary disease, cirrhosis, and cystic fibrosis (acute phase)
CA72-4	Cancer antigen 72-4	Used as an aid for monitoring response to treatment and for detecting the recurrence of disease	Ovarian, breast, colon, endometrial, gallbladder, and pancreatic cancer. Elevated levels in rheumatoid arthritis and ovarian cysts
AFP	Alpha fetoprotein	Used as an aid to assess response to cancer treatment	Nonseminomatous germ cell tumours, hepatocellular carcinoma, colon, pancreatic, and biliary cancers. Elevated in benign conditions, such as viral hepatitis, cirrhosis, and pregnancy
b-HCG	Free beta-subunit of human choriogonadotropin	Used as an aid to assess response to cancer treatment	Testicular, ovarian, trophoblastic tumours (choriocarcinomas and invasive hydatidiform moles), pancreatic, lung, bladder, and, rarely, lymphoma and breast cancers. Elevated in benign conditions, such as hypogonadal states, marijuana use; rarely, it is elevated during pregnancy and in postmenopausal women
PG I/II	Pepsinogen I/II ratio	Used as aid for detecting atrophic gastritis	-
HER2/neu	Receptor tyrosine-protein kinase erbB-2, ERBB2	Used as an aid in the selection of appropriate treatment and monitoring treatment responses	Breast (primary or metastatic), lung, bladder and pancreatic cancers, Wilm’s tumour