The repeated exposure of a normal cell to carcinogenic agents may lead to its mutation, which changes into a cancer cell. In this case, the structure and function of the cells would alter, and they do not act normally. Chemicals, sun exposure, shortwaves, viruses, and bacteria play a significant role in cancer. Among the infectious and bacterial agents causing cancer, Helicobacter pylori (H. pylori) is the most important bacterium involved in carcinogenesis. H. pylori causes chronic gastritis, peptic ulceration, and gastric cancer. Recently, this bacterium has been classified as class I carcinogen (i.e., a definite cause of cancer in humans). Despite the pathogenic effect of this bacterium, it has been recently affirmed to induce apoptosis in cancer cell line and affect the reduction of tumor size in animal models. This result suggests that some factors of H. pylori can be used as a new tool in future therapeutic strategies implemented in cancer immunotherapy.