Although some evidence has validated the connection between heterogeneous nuclear ribonucleoprotein C (HNRNPC) and the progression of tumors, a pan-cancer investigation is still required. Thus, we explored the oncogenic effect of HNRNPC across many tumors using The Cancer Genome Atlas datasets. Moreover, short hairpin RNAs (shRNAs) were found to repress HNRNPC in lung adenocarcinoma (LUAD) cells, and the effect on LUAD cells proliferation and metastasis was examined using a Cell Counting Kit-8, transwell, and invasion test. HNRNPC was found to be overexpressed in most cancers, and a divergent relationship was observed between the abnormal levels of HNRNPC and tumor prognosis. HNRNPC level was observed to correlate with the cancer-associated fibroblast infiltration, such as lung cancer. Furthermore, higher HNRNPC levels were found in LUAD tissues and cells. Subsequently, Kaplan-Meier analysis revealed that the increased HNRNPC level was connected with worse overall survival and disease-free survival in LUAD patients. Moreover, HNRNPC silencing reduced the progression of A549 and H1299 cells, including proliferation, migration, and invasion. This is the first pan-cancer investigation that presents a relatively systematic finding of the oncogenic effect of HNRNPC among many cancer types. Our data indicate that HNRNPC facilitates the biological processes of LUAD cells; nevertheless, further research on the mechanism underlying the role of HNRNPC in LUAD development is warranted.