The object is elucidate the role of a PRDM family on cancer and to provide a novel therapeutic agent for cancer associated with PRDM and a method for detection of the cancer. Thus, provided are: a therapeutic agent for breast or ovarian cancer, which comprises an inhibitor of the expression of PRDM14 gene or an inhibitor of PRDM14; and a method for detecting breast or ovarian cancer in a subject based on the level of the expression of PRDM14 gene in a biological sample collected from the subject.