Ductal Carcinoma In Situ With Microinvasion Arising in a Breast Hamartoma: A Case Report and Review of Guidelines of Hamartoma Management

Breast hamartomas are rare, benign lesions composed of adipose, fibrous and glandular tissue. While typically non‐malignant and not linked to increased breast cancer risk, they are often underdiagnosed due to variable imaging and histological features. We report a rare case of ductal carcinoma in situ (DCIS) with microinvasion arising within a mammary hamartoma. Unexpectedly the patient went on to develop a triple‐negative invasive breast cancer 6 months following nipple‐sparing mastectomy and implant reconstruction. To date, only 16 cases of breast carcinoma within hamartomas have been reported, making this case an important addition to the limited literature. It highlights the need for careful imaging interpretation, pathological review and multidisciplinary management, particularly in lesions with glandular components or atypical features. With increasing use of breast imaging, identification of hamartomas is expected to rise, making awareness of their rare malignant potential essential. In the absence of prevalence data or management guidelines, this case underscores the value of centralised reporting and collaborative clinical decision‐making.