What happened, in summary

This 69-year-old woman had chronic kidney disease since 2009 and had been on twice-weekly maintenance hemodialysis for 4 years. In July 2021, she came to an oncology clinic after noticing a left breast lump for about 1 month. Mammography showed a 3 × 2 cm mass in the central and lower outer quadrants. Ultrasound-guided core biopsy confirmed grade II invasive ductal carcinoma. Pathology showed hormone receptor-positive, HER2/neu-positive, E-cadherin-positive disease with Ki-67 expression of 55-60%, consistent with luminal B breast cancer. PET-CT showed the left breast mass with left axillary lymphadenopathy, and the clinical stage was cT2N1M0. Her kidney disease shaped treatment decisions. Conventional chemotherapy with HER2-targeted therapy was not chosen because of renal compromise, and she was also concerned about chemotherapy-related hair loss and treatment tolerability. After discussion, she chose trastuzumab emtansine, or T-DM1, at 3.6 mg/kg every 3 weeks, given alongside alternate-day hemodialysis. She tolerated treatment well. After 6 cycles, PET-CT showed a good documented partial response, with decreased size and metabolic activity of the breast lesion and metabolic resolution of left level-I axillary nodes. She then underwent modified radical mastectomy. Pathology showed residual grade II invasive ductal carcinoma measuring 1.2 cm, with 1 of 25 lymph nodes positive, staged ypT1cN1aMx. Because there was residual disease, T-DM1 was continued to complete 1 year of anti-HER2 therapy. She completed 12 total cycles without reported adverse events. As of March 2023, PET-CT from May 2022 showed no metabolically active disease. She then started endocrine therapy and continued dialysis.