However, the expression of PIWIL2 has been observed in various types of primary cancers and tumor cell lines [1, 11], including breast cancer [20], cervical cancer [21], gastric cancer [22],acute myeloid leukemia [23], colorectal cancer [24], colon cancer [24, 25], ovarian cancer [26] and testicular germ cell tumors [11, 27], etc. This evidence concerns the gene PIWIL2 and cancer.