Stage IIIC ER-positive male breast cancer: mastectomy, chemotherapy, radiation, tamoxifen and abemaciclib

What happened, in summary

A 43-year-old Japanese man developed itchy erosion of the left areola that did not improve after 3 months of topical treatment for presumed dermatitis. Skin biopsy showed invasive ductal carcinoma of no special type. The tumor was hormone-receptor positive, with ER 90% and PR 60%, HER2 score 0, and Ki-67 15%. His medical history included type 2 diabetes, hypertension, panic disorder, and mood disorders that were controlled with medication; he did not smoke or drink alcohol. Tumor markers were normal, hemoglobin A1c was 7.2%, and BRCA1/2 testing found no pathogenic variants. MRI and CT showed locally advanced left breast cancer with axillary lymph-node metastases up to level II and no distant metastasis. Before surgery, the cancer was staged cT4bN1aM0, Stage IIIB. He underwent left mastectomy with level I-III axillary lymph-node dissection. Pathology showed a 50-mm invasive ductal carcinoma with skin ulceration, negative margins, and extensive nodal disease: 16 of 17 axillary lymph nodes were positive. Final stage was pT4bN3aM0, Stage IIIC. Postoperative treatment included dose-dense doxorubicin plus cyclophosphamide, followed by weekly paclitaxel and postmastectomy radiation therapy to 50 Gy. He then began tamoxifen plus abemaciclib as adjuvant endocrine and targeted therapy. Abemaciclib started at 150 mg twice daily, but within 2 weeks he developed severe diarrhea, more than 8 episodes daily, and the dose was reduced to 100 mg/day. Continued diarrhea and elevated creatinine led to a further reduction to 50 mg/day, while cystatin C suggested preserved renal function. He continued tamoxifen and abemaciclib, and annual follow-up imaging showed no local or distant recurrence.