Triple-negative breast cancer in remission after chemotherapy and pembrolizumab

What happened, in summary

A 53-year-old woman with triple-negative breast cancer had tumor biology confirmed as ER-negative, PR-negative, and HER2-negative. Her original anatomic stage was not stated. She completed 16 cycles of chemotherapy, including doxorubicin and cyclophosphamide, followed by taxane-based therapy, and achieved remission. Pembrolizumab was then started as maintenance therapy. She had no prior history of adrenal insufficiency or other major endocrine disorder. After 8 cycles of pembrolizumab, she developed dizziness, fatigue, and shortness of breath while on a cruise. Testing on the ship showed severe hyponatremia, with sodium of 117 mEq/L, and she was transferred to a hospital. In the emergency department, blood pressure was 90/60 mmHg, heart rate was 75 beats per minute, and she remained alert and oriented. Laboratory testing showed high ACTH with low cortisol, supporting primary adrenal insufficiency, or Addison’s disease. Thyroid function was normal, and oncology PET-CT showed no new primary or secondary tumors, including no adrenal involvement. She received intravenous hydrocortisone and sodium replacement, with rapid symptom improvement and sodium stabilization. She was discharged on oral hydrocortisone with endocrinology follow-up. The Naranjo adverse-drug-reaction assessment gave pembrolizumab a score of 4, supporting a possible relationship to the adrenal insufficiency. Her cancer remained in remission, but her survivorship care now required ongoing steroid replacement planning, monitoring for recurrent hyponatremia, and coordination between oncology and endocrinology. The case also noted relatively low IGF-1 and possible pituitary involvement, but the working diagnosis remained primary adrenal insufficiency with severe hyponatremia. The rapid response to hydrocortisone and sodium replacement separated the endocrine emergency from cancer relapse.