How I Treat: A Woman with HR+/HER2-Negative Breast Cancer
Arielle Medford, MD
Introduction. A 63-year-old woman presented for care after palpating a left-sided breast mass. She did not have a significant past medical history.
Diagnostic examination. Diagnostic mammogram and ultrasound identified a 6 cm breast mass. Biopsy identified a grade 2 invasive lobular carcinoma, estrogen receptor (ER)-positive (90%)/progesterone receptor (PR)-positive (90%)/human epidermal growth factor receptor 2-negative (HER2-negative) breast cancer (immunohistochemistry 2+, Fluorescence In Situ Hybridization-negative). Review of systems was unremarkable.
Physical examination. The patient’s physical examination was notable for a palpable 6 cm left breast mass without skin changes and no palpable lymph nodes. Genetic testing was negative for germline mutations, including BRCA1/2.
Treatment and management. She went to surgery and underwent a left mastectomy with sentinel lymph node biopsy. Final pathology removed a 5.5 cm invasive lobular carcinoma, ER+/PR+/HER2-, grade 2, with negative margins. Two lymph nodes were removed, and one had metastatic disease. Oncotype DX testing was sent and resulted in a risk recurrence score of 7.
Because she was postmenopausal and had one to three positive lymph nodes with an Oncotype DX score < 26, she did not receive chemotherapy, per the RxPonder trial.1 After completing radiation, she started an aromatase inhibitor for adjuvant endocrine therapy, with a plan to continue for 5 years to 10 years. Next, we discussed with the patient potentially adding the CDK4/6 inhibitor, abemaciclib, to her adjuvant regimen, with a plan to continue for 2 years. In 2021, the FDA approved abemaciclib to be used as adjuvant therapy for high-risk, lymph-node positive, HR-positive, HER2-negative breast cancer. Approval was based on the monarchE trial, which showed improvement in 3-year invasive disease free survival compared to endocrine therapy alone (89% vs 83%, hazard ratio [HR] = 0.70, [95% CI, 0.59 to 0.82]) and distant recurrence-free survival (90% vs 86%, HR = 0.69 [95% CI, 0.57 to 0.83]).2 After starting abemaciclib, she developed diarrhea, a common side effect, which she treated with loperamide.
