Metastatic neuroendocrine neoplasms of the breast: a systematic review

Neuroendocrine neoplasms (NENs) originate mainly in the digestive system and lungs and are classified as neuroendocrine carcinomas (NECs) or neuroendocrine tumors (NETs). Breast metastases from NENs are rare, accounting for only 1% of breast neoplasms, but may be more frequent than expected. This study aimed to characterize patients with breast metastatic NENs through a literature review. A systematic review was conducted using PubMed, Embase, LILACS, and OpenGrey databases through July 2024. Eligible studies included case reports, case series, or cross-sectional studies documenting at least one breast metastatic NEN case confirmed by histopathology or imaging. Eighty-one articles with 138 cases were included. The mean age was 52.9 (SD 12.18) years, and three patients were male. NETs were more common than NECs (82.6 vs 14.5%), and the small intestine was the primary site in 45.3% of cases, followed by the lung (26.6%). Breast lesions were the first clinical manifestation in 24.8% of cases. Carcinoid syndrome symptoms occurred in 21.4% of patients. Ultrasonography revealed hypoechoic lesions with irregular margins, and mammography showed poorly defined margins. Chemotherapy was used in 57.4% of patients, typically with etoposide and platinum, and somatostatin analogs were administered to 36.2% of patients. Surgical resection of the primary tumor occurred in 74.6% of cases, and metastasis resection occurred in 73.5%. This review highlights the importance of accurate diagnosis, as a significant number of cases were initially misdiagnosed as primary breast tumors. Proper diagnostic evaluation can improve patient outcomes.