Stage 3 triple-negative breast cancer complicated by immunotherapy endocrine toxicity

What happened, in summary

This 49-year-old woman was diagnosed with triple-negative breast cancer after mammography and ultrasound found a left upper-outer breast mass and a suspicious axillary lymph node. On clinical exam, the tumor was larger than on imaging, and PET showed FDG uptake in the breast lesion and axillary node without distant metastases. Core biopsy showed invasive ductal carcinoma that was ER-negative, PgR-negative, HER2 0, and high-proliferation with Ki-67 70%. The clinical stage was cT2N+M0, and she started neoadjuvant KEYNOTE-522-based treatment: pembrolizumab, carboplatin, and paclitaxel, followed by pembrolizumab with cyclophosphamide and epirubicin. By the second cycle, fever, vomiting, and marked fatigue led to discontinuation of carboplatin. Liver dysfunction also required paclitaxel dose reduction. After 4 cycles, routine labs showed severe hypothyroidism, and levothyroxine was started. Pembrolizumab was held at the beginning of the next phase, then reintroduced after endocrinology review. After the second cycle of epirubicin and cyclophosphamide, she developed fever, fatigue, muscle pain, nausea, appetite loss, and very low cortisol, leading to cortisone acetate replacement. Suspected immune-related hypophysitis was evaluated with brain MRI, and hormone replacement continued. Pembrolizumab was omitted from the third and fourth cycles. Surgery on December 17, 2024 showed residual triple-negative invasive carcinoma, ypT1c ypN0, with no metastases in 22 removed lymph nodes. Because pembrolizumab was contraindicated, she received adjuvant capecitabine for 8 cycles, completed in June 2025. Ongoing care focused on cancer follow-up and management of thyroid and adrenal hormone replacement. This sequence left her with both residual cancer risk and chronic immune-endocrine effects requiring coordinated follow-up.