An otherwise healthy 58-year-old woman with a history of breast cancer presents to the clinic with newly diagnosed metastatic disease. Nine years prior, she received a diagnosis of left-sided, stage IIIA (T2N2M0), grade 1 infiltrating lobular carcinoma (ILC). She was premenopausal at the time. Her original breast biopsy revealed ILC, with estrogen receptor (ER) positivity (44%), progesterone receptor (PR) negativity, and human epidermal growth factor receptor 2 (HER2) negativity by fluorescence in situ hybridization (FISH). Left mastectomy was completed, and an axillary lymph node dissection showed a 4.0-cm tumor and 6/12 positive axillary nodes. Postoperative staging with PET/CT showed no evidence of distant metastatic disease. She completed 6 cycles of adjuvant docetaxel, doxorubicin, and cyclophosphamide chemotherapy followed by postmastectomy chest wall and regional nodal radiation, and was started on tamoxifen. A contralateral risk-reducing mastectomy and bilateral salpingo-oophorectomy were completed about 1 year after diagnosis. The patient stopped her adjuvant tamoxifen after approximately 1 year due to side effects and loss of health insurance.
Recently, the patient developed increasing abdominal pain, bloating, and constipation with smaller-caliber stools. Abdominal CT showed a mass in the transverse colon with ascites and peritoneal nodularity (Figure). No obvious liver metastasis or cirrhosis were present. Colonoscopy was attempted, but the stricture resulting from the colon mass was unable to be traversed. A palliative exploratory laparotomy with subtotal colectomy was performed due to impending complete obstruction. The pathology report revealed infiltration of poorly differentiated carcinoma—most consistent with breast primary—in the sampled small intestine, large intestine, appendix, and mesentery. Margins were positive. Immunologic stains were positive for mammaglobin, GATA binding protein 3 (GATA-3), and cytokeratin 7 (CK7). The sample was positive for ER (3+, 90%) and PR (3+, 5%) but negative for HER2. Following surgery, the patient’s normal bowel function returned, and she was referred to oncology for treatment of her newly diagnosed metastatic breast cancer.
Which of the following represents the best initial systemic treatment for this patient?
A. Letrozole + palbociclib
B. Letrozole alone
C. Fulvestrant + abemaciclib
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