The male breast cancer (MBC) is a rare and represents less than 1% of all malignancies in men and only 1% of all breast cancers incident (1). When it spreads, the gastrointestinal tract is rarely involved, and rectal metastasis is exceptionally unusual (2,3). Occult breast cancer (OBC) adds another layer of complexity. OBC is defined as a clinically recognizable metastatic carcinoma arising from an undetectable primary breast tumor and was first described by Halsted in 1907 (4).  It is thought that OBC is secondary to microinvasive breast cancer (5).It presents in 0.3–1 % of all breast cancers (6), with first presentation by axillary and cervical lymph node metastases (7). It is usually identified only after biopsy of a metastatic site, supported by immunohistochemical markers (8).

Here, we report the case of a 43-year-old man with a strong family history of colorectal cancer who underwent a screening colonoscopy despite being entirely asymptomatic. During colonoscopic evaluation, a small erythematous, slightly elevated rectal lesion measuring approximately 10 × 8 mm was incidentally identified at about 7 cm from the anal verge. The lesion showed no ulceration and was surrounded by a mildly thickened rectal wall. Targeted biopsies were obtained.

Histopathological examination, supported by immunohistochemical profiling, revealed adenocarcinoma consistent with metastatic breast origin—an unexpected finding in a male patient with no prior history of breast disease. Subsequent staging with dedicated breast imaging and PET-CT confirmed the diagnosis of occult breast cancer with metastatic involvement of the rectum, regional lymph nodes, and bone.

This case underscores the critical value of colonoscopy not only for colorectal cancer prevention in high-risk individuals but also for detecting unexpected metastatic disease in asymptomatic patients.