<s>[INST] context: The diagnosis of ovarian cancer is often delayed, because symptoms often do not occur until late in the disease when the mass is large and applies pressure to other abdominal organs. The symptoms illustrated in the case are typical. Patients may also develop ascites with shoness of breath, a variety of gastrointestinal symptoms related to impaired motility secondary to pressure, and, if the ovarian cancer is a type that secretes hormones, menstrual irregularities or abnormal hair growth. The most widely studied tumor marker in ovarian cancer is CA-125. This marker is not of paicular use in screening of the general population for two reasons: 1) small cancers often do not cause serum elevations of the marker; and 2) serum levels of the marker can be elevated by a variety of cancers (including those of ovary, breast, pancreas, colon, and lung) and benign conditions (including endometriosis, pregnancy, liver disease, and congestive hea failure). However, if there is already a strong suspicion or a known history of ovarian cancer, CA-125 can be helpful in establishing if the cancer burden (if present) is large, and whether following the CA-125 levels following surgery can be used to monitor for recurrent disease. While small tumors are not always picked up (50% of women with small ovarian cancers have normal CA-125), more than 80% of women with advanced ovarian cancer have CA-125 elevations. Adrenocoicotropic hormone can be elevated in ectopic hormone-producing lung cancers. Galactosyltransferase can be elevated in a wide variety of cancers, including those from lung, breast, esophagus, stomach, pancreas, and colon. It is not used as a marker for ovarian cancer. S-100 is a marker for melanoma and neuroendocrine tumors. [/INST] question: A 57-year-old woman presents to a physician with chronic pelvic pain of many years duration. On fuher questioning, the woman also repos urinary frequency, constipation, pain with intercourse and bloating. On physical examination, a large mass is felt in the pelvic area. Follow-up ultrasound examination demonstrates that the mass involves the right adnexa and is composed of multiloculated cystic spaces. Prior to sending the patient to surgery, the primary care physician wants to order a serum tumor marker to screen for ovarian cancer. Which of the following would be the best choice? | options: A: Adrenocoicotropic hormone B: CA-125 C: Galactosyltransferase D: S-100 | answer: B </s>