A 57-year-old postmenopausal woman comes to the office due to vaginal spotting and increasing pelvic pressure. For the past few months, the patient has had pelvic pressure with some associated constipation, for which she takes fiber supplements with no relief. For the last week, she has also had vaginal spotting and occasional passage of small blood clots. The patient was diagnosed with breast cancer 3 years ago and has been taking tamoxifen for the past 2 years because she could not tolerate the adverse effects of aromatase inhibitors. She has no other chronic medical conditions, and her only surgeries were 3 cesarean deliveries in her 30s. Vital signs are normal. BMI is 23 kg/m². A large, irregular mass is palpable above the symphysis pubis, but there is no fluid wave or tenderness to palpation. On pelvic examination, there are no cervical or vaginal lesions; a small amount of blood is seen at the cervical os. The uterus appears well supported and does not descend with the Valsalva maneuver. Which of the following is the most likely diagnosis in this patient?

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11ec25c8_d9ef_05d7_bc81_590766f6a0b4_MD0003_00 This patient with postmenopausal bleeding and a pelvic mass most likely has a uterine sarcoma, a rare but aggressive malignancy. Uterine sarcoma typically presents with a uterine mass (as in this patient's enlarged, irregularly shaped uterus) that causes bulk symptoms (eg, pelvic pressure, constipation) and abnormal or postmenopausal bleeding. Uterine sarcoma is often indistinguishable from benign leiomyomata (ie, uterine fibroids); however, it should be suspected in postmenopausal women who have taken tamoxifen or have other risk factors (eg, pelvic radiation). Tamoxifen is a selective estrogen receptor modulator used as an adjuvant treatment for breast cancer. Although tamoxifen has antagonist effects on the breast, it has estrogen agonist effects on the uterus and therefore increases the risk of uterine sarcoma and endometrial hyperplasia or cancer. For this reason, the FDA has issued a black box warning for patients and providers but recognizes that the benefits of tamoxifen therapy typically outweigh the risks for most patients with breast cancer. (Choice A) Adenomyosis can present with an enlarged uterus and abnormal uterine bleeding (eg, heavy menses); however, patients have a symmetrically enlarged, globular uterus, not an irregular uterine mass. Adenomyosis (Choice B) Choriocarcinoma (ie, gestational trophoblastic neoplasia) can present with an enlarged uterus and abnormal uterine bleeding after pregnancy. Choriocarcinoma affects women of childbearing age, making this diagnosis unlikely in this patient. (Choice C) Metastatic cancer to the ovaries can cause a pelvic mass and bulk symptoms; however, it is typically associated with ascites (ie, fluid wave on palpation), which is not seen in this patient. In addition, breast cancer preferentially metastasizes to the lungs, liver, and bones, making this diagnosis less likely. (Choice D) Pelvic organ prolapse (eg, complete procidentia) can cause pelvic pressure, constipation, and postmenopausal bleeding due to exposed, eroded vaginal mucosa. However, it typically presents with a vaginal, not abdominal, mass. In addition, this patient's uterus is well supported, making this diagnosis unlikely. procidentia (Choice E) Sarcoma botryoides, a type of embryonal rhabdomyosarcoma, can present as a genitourinary mass, but it is typically vaginal and exclusively diagnosed in infants, not postmenopausal patients. Sarcoma botryoides Educational objective: Uterine sarcoma typically presents with postmenopausal bleeding and a uterine mass that causes bulk symptoms (eg, pelvic pressure, constipation). Tamoxifen use is a significant risk factor due to its estrogen agonist effects on the uterus. References: Committee opinion no. 601: tamoxifen and uterine cancer. (http://www.ncbi.nlm.nih.gov/pubmed/24848920) Uterine sarcoma after tamoxifen therapy for breast cancer. (http://www.ncbi.nlm.nih.gov/pubmed/24282897)

A 57-Year-Old Postmenopausal Woman Comes to the Office Due to Vaginal