Invasive lobular carcinoma of the breast with multifocal gastrointestinal, ovarian, and peritoneal metastases: a case report.

backgroundInvasive lobular carcinoma of the breast exhibits distinct biological behavior and metastatic patterns compared with invasive ductal carcinoma, with a recognized tendency to involve unusual sites such as the gastrointestinal tract, peritoneum, and ovaries. These metastases are often clinically occult and may mimic primary gastrointestinal or gynecologic malignancies, leading to delayed diagnosis. CASE PRESENTATION: We report the case of a 43-year-old Iranian woman with estrogen receptor-positive invasive lobular carcinoma who developed sequential multifocal metastases to the stomach, ovaries, peritoneum, rectum, and jejunum over a 9-year disease course. Initial biochemical progression, manifested by a rising serum cancer antigen 15-3 level, preceded overt radiologic or endoscopic findings. Gastric metastasis was confirmed by biopsy 6 years after primary treatment. Despite negative pelvic imaging, bilateral salpingo-oophorectomy revealed occult ovarian and peritoneal metastases. Subsequent rectal and small-bowel involvement were diagnosed following new gastrointestinal symptoms. The patient was managed with multiple lines of systemic therapy and remains under active treatment with disease confined to the abdominal cavity.

conclusionThis case highlights the insidious metastatic behavior of invasive lobular carcinoma and the limitations of conventional imaging in detecting gastrointestinal and ovarian involvement. Persistent or unexplained gastrointestinal symptoms and rising tumor markers in patients with a history of invasive lobular carcinoma should prompt consideration of metastatic disease and early histopathological evaluation.