APOD and breast cancer: These DDR-related genes have been studied and found to affect tumor biological behavior in a variety of cancer types, of which we are particularly interested in the risk gene with the highest mutation rate, APOD, whose expression product is tumor apolipoprotein D. Upregulation of APOD expression has been reported to promote the progression of breast cancer [41] and prostate cancer [42], and it may be an important risk gene for gastric cancer.