The most studied marker for ovarian cancer, CA125, is a protein that is found at levels in most ovarian cancer cells that are elevated compared to normal cells and a potentially useful marker for diagnosis and prognosis after treatment of ovarian cancer, but CA125 is expressed in only 50–60% of patients with early-stage disease, and is also frequently elevated in women with benign ovarian diseases [20]–[22]. The gene discussed is MUC16; the disease is ovarian cancer.