Unusual metastatic sites of breast cancer in five patients: a case series

Breast cancer (BC) is the most common cancer in women worldwide and a leading cause of cancer-related mortality. Approximately 7% of cases are metastatic at diagnosis. While bone, lung, liver, brain, and supradiaphragmatic lymph nodes are common metastatic sites, metastases to unusual locations such as the genitals, gastrointestinal tract, or soft tissues are extremely rare (less than 1–3%). These atypical patterns can pose diagnostic and therapeutic challenges, as they may mimic other diseases or remain asymptomatic until advanced stages. Recognizing these rare metastases is essential for timely diagnosis and optimal management. We conducted a retrospective study at our institute, reviewing BC patients who developed metastases at rare locations between 2015 and 2024. Clinical, radiological, and pathological data were collected and analyzed. Cases were included based on the rarity of the metastatic site and the availability of complete clinical information. We report five cases of breast cancer in Tunisian patients of North African ethnicity who developed metastases at unusual sites: Vulvar metastasis in a 51-year-old woman, occurring nine years after the initial diagnosis, with concurrent bone and pulmonary metastases. Gingival metastasis in a 42-year-old woman, ten years after treatment for hormone receptor-positive BC. Inguinal lymph node metastases in two patients: one presented with concomitant hepatic metastases, whereas the other initially had isolated inguinal lymph node metastasis and subsequently developed retroperitoneal and pelvic lymph node metastases 22 months after the diagnosis of the inguinal metastasis. Choroidal metastasis in a 61-year-old man with ER-positive invasive ductal carcinoma, presenting with decreased visual acuity 6 months post-surgery (8 months after initial diagnosis); further metastatic spread was detected 18 months after diagnosis. These cases illustrate the diversity of metastatic presentations in BC and highlight the importance of continuous surveillance. New or atypical lesions, even at rare sites, should prompt consideration of metastasis. Imaging findings should be interpreted cautiously, and histological confirmation via biopsy is recommended when diagnostic uncertainty exists. Early recognition and individualized management strategies may help optimize patient care in these complex situations.