Metastatic breast involvement from extramammary malignancies: a review of dissemination pathways, imaging features, and management strategies.

Metastatic involvement (MB) of the breast from extramammary malignancies is rare, with an incidence of 0.09-1.3% of all breast malignancies. Due to its variable clinical and radiological presentation, MB often mimics primary breast cancer (BC), leading to potential misdiagnosis and impacting treatment decisions. This narrative review analysed MB cases based on dissemination pathways: hematogenous (HM), lymphatic (LM), or direct contiguous (DC) spread. HM was the most frequent, particularly in melanoma, lung, renal, and gastrointestinal carcinomas, presenting as well-circumscribed, non-calcified nodules without axillary lymph node involvement, distinguishing them from BC. LM spread, common in HM malignancies, caused diffuse breast oedema, skin thickening, and a "peau d'orange" appearance, resembling inflammatory BC. DC spread, though rarer, was observed in advanced lung cancer, with infiltrative lesions extending from the chest wall. Multimodal imaging (Mammography (DM), Ultrasound (US), Magnetic Resonance Imaging (MRI), Computer Tomography (CT), and Positron Emission Tomography (PET)) was critical for detecting MB, while histopathological and immunohistochemical analysis confirmed extramammary origin. Due to the rarity and heterogeneity of MB, diagnosis requires a multidisciplinary approach integrating oncological history, imaging, and pathology. Recognising distinct imaging patterns can aid early diagnosis, avoid unnecessary surgery, and guide appropriate systemic therapy based on the primary malignancy. Early identification of the metastatic pattern may influence clinical management decisions and improve patient outcomes.