Breast cancer metastasis to the colon mimicking primary colorectal carcinoma.

Breast cancer metastasis to the colon is rare, occurring in less than 1% of patients with metastatic breast cancer. Invasive lobular carcinoma (ILC) exhibits a distinct tropism for the gastrointestinal tract and adnexa, often presenting with atypical imaging features that mimic primary tumors. We report a case of a 58-year-old woman with a history of right breast ILC who presented with incidental pelvic masses on ultrasound five years after mastectomy. 2-[¹⁸F]FDG PET/CT revealed multifocal hypermetabolic lesions in the transverse colon wall and bilateral adnexa. CT enterography and colonoscopy confirmed a stenotic colonic lesion with smooth mucosa. Postoperative pathology following right hemicolectomy, hysterectomy, and bilateral salpingo-oophorectomy confirmed metastatic breast carcinoma involving the right colon and bilateral adnexa. This case highlights the critical role of PET/CT in detecting occult gastrointestinal metastases in patients with ILC and underscores the importance of considering metastatic disease in the differential diagnosis of colonic lesions in this population.