Metastatic Carcinoid Presenting as a Breast Lesion

Metastasis to the breast is a rare occurrence, constituting fewer than 2% of all breast tumours. Of all metastatic tumours in the breast, most arise from contralateral breast primaries. Other reported primary solid tumour sites include melanoma; lung, gastric, and renal cancers; and approximately 29 cases of carcinoid tumour. Ambiguous presentations and an absence of carcinoid syndrome features make accurate radiographic and histologic assessment of breast carcinoids challenging. Here, we report the case of a 52-year-old woman who presented with a mammographic abnormality in the left breast. Excisional biopsy revealed histopathology consistent with carcinoid. After an exhaustive work-up, carcinoid within the terminal ileum was ultimately identified, and the woman was diagnosed with metastatic breast carcinoid, an exceedingly rare entity. This paper describes the common mammographic, cytologic, and immunohistochemical features typical of metastatic breast carcinoid tumours, together with their common clinical features, prognosis, and treatment options.