Carcinomas of the breast with endocrine differentiation: a review

The occurrence of endocrine differentiation in some mammary carcinomas seems well-established, but pathologists continue to debate its significance. Contemporary thinking suggests that endocrine tumours of the breast do not constitute a single clinicopathological entity with a consistent histogenesis but rather that endocrine differentiation represents a pathway of neoplastic development available to a range of breast cancers. This pattern of differentiation occurs in tumours with vastly different morphological appearances, such as: ductal carcinoma in situ, mucinous carcinoma, a variant of lobular carcinoma, and low grade invasive ductal carcinoma. Although such tumours share some characteristics with intestinal endocrine neoplasms, the typical pattern of intestinal carcinoid virtually never occurs in mammary lesions. Conventional microscopy permits the diagnosis in most cases. Specialized techniques (histochemistry, immunohistochemistry, and electron microscopy) can serve as the basis for diagnosis in the absence of the appropriate morphological features. Although the system of nomenclature proposed by the World Health Organization for use with endocrine tumours in other organs can be used for endocrine tumours of the breast, only a minority of lesions will fit the established criteria. Most lesions are classifiable in the conventional categories of mammary carcinomas. No special prognostic significance is attached to these tumours at the present time.