Neuroendocrine Breast Cancer-Associated Ectopic Adrenocorticotropic Hormone Syndrome Requiring Bilateral Adrenalectomy

Ectopic adrenocorticotropic hormone syndrome (EAS) occurs when a tumor develops neuroendocrine differentiation with the secretion of ACTH resulting in hypercortisolism and possibly Cushing's syndrome (CS). Only 5-10% of CS cases are attributed to EAS; of these, breast tumors comprise less than 1%. Two known variants of breast neuroendocrine tumors include neuroendocrine-differentiated carcinoma and ductal carcinoma with neuroendocrine features. Currently, guidelines for treatment are limited and EAS is associated with significant morbidity and mortality. A 39-year-old female presented with a rapidly enlarging breast mass. Biopsy demonstrated invasive poorly differentiated breast carcinoma with high-grade neuroendocrine features and necrosis. Staging at diagnosis confirmed metastatic disease of the liver and bone. First-line chemotherapy (Cisplatin/Etoposide/Durvalumab) was initiated with evidence of disease progression after four cycles. Given a poor response to therapy, a simple mastectomy was performed for local control and complete pathologic analysis, demonstrating high-grade neuroendocrine carcinoma with large-cell features. Second-line therapy (Adriamycin/Cyclophosphamide) was initiated for three cycles after which the patient required admission for severe and refractory hypokalemia. Workup confirmed elevated ACTH consistent with paraneoplastic EAS and further evidence of disease progression. Third-line therapy (Nab-Paclitaxel) was initiated, and genetic testing was completed, confirming the PIK3 mutation, for which access to Alpelisib therapy was requested. Given symptoms of progressive severe CS with significant liver disease limiting medical therapies, the patient underwent urgent bilateral laparoscopic adrenalectomy after which she was able to be discharged home while awaiting additional systemic therapy. EAS resulting in CS secondary to breast neuroendocrine carcinoma is a rare and challenging diagnosis. Further research is needed to inform treatment guidelines to improve outcomes. While patient survival is dependent upon the underlying disease process, laparoscopic bilateral adrenalectomy is an accepted, definitive treatment option.