BACKGROUND: It is well known that pepsinogen (PGs), as an important precursor of pepsin performing digestive function, has a good correlation with the occurrence and development of gastric cancer and it is also known that ectopic PGs expression is related to the prognosis of some cancers. However, the panoramic picture of pepsinogen gene family in human cancer is not clear. This study focused on elucidating the expression profile, activated pathway, immune cells infiltration, mutation, and copy number variation of PGs and their potential role in human cancer. METHOD: Based on the next generation sequence data from TCGA, Oncomine, and CCLE, the molecular changes and clinical correlation of PGs in 33 tumor types were analyzed systematically by R language, including the expression, mutation, and copy number variation of PGs and their correlation with cancer-related signal transduction pathway, immune cell infiltration, and prognostic potential in different cancers. RESULTS: PGs expression profiles appear different in 33 tumors. The transcriptional expression of PGs was detected in 16 of all 33 tumors. PGC was highly expressed in cholangiocarcinoma, colon adenocarcinoma, rectum adenocarcinoma, uterine corpus endometrial carcinoma, bladder urothelial carcinoma and breast cancer, while decreased in stomach adenocarcinoma, kidney renal clear cell carcinoma, prostate adenocarcinoma, lung squamous cell carcinoma, and esophageal carcinoma. PGA3, PGA4, and PGA5 were expressed in most normal tissues, but decreased in cancer tissues. PGs expression was significantly related to the activation or inhibition of many signal transduction pathways, in which PGC and PGA5 are more likely to be associated with cancer-related pathways. PGC participated in 33 regulatory network pathways in pan-cancer, mainly distributed in stomach adenocarcinoma, esophageal carcinoma, and lung squamous cell carcinoma, respectively. PGC and PGA3 expression were significantly correlated with immune cell infiltration. The results of survival analysis showed that different PGs expression play significantly different prognostic roles in different cancers. PGC was correlated with poor survival in brain lower grade glioma, skin cutaneous melanoma, and higher survival in kidney renal clear cell carcinoma, acute myeloid leukemia, mesothelioma, and uveal melanoma. PGA4 was only associated with higher survival in kidney renal clear cell carcinoma. Genetic variation analysis showed that PGC gene often mutated in uterine corpus endometrial carcinoma and stomach adenocarcinoma had extensive copy number amplification in various tumor types. PGC expression was upregulated with the increase of copy number in cholangiocarcinoma, esophageal carcinoma, and kidney renal papillary cell carcinoma, while in stomach adenocarcinoma, PGC was upregulated regardless of whether the copy number was increased or decreased. CONCLUSIONS: PGs was expressed unevenly in a variety of cancer tissues and was related to many carcinogenic pathways and involved in the immune regulation. PGC participated in 33 regulatory pathways in human cancer. Different PGs expression play significantly different prognostic roles in different cancers. The variation of copy number of PGC gene could affect the PGC expression. These findings suggested that PGs, especially PGC have characteristic of broad-spectrum expression in multiple cancers rather than being confined to the gastric mucosa, which may made PGs be useful biomarkers for prediction/diagnosis/prognosis and effective targets for treatment in human cancer.