Concurrent invasive ductal carcinoma and ductal carcinoma in situ arising inside and outside a breast hamartoma: A case report.

Background: Breast hamartomas are rare benign breast tumors, with an incidence rate of 0.8%-4.8%. Further, the coexistence of hamartomas and carcinoma is also uncommon. Our case report presents a unique instance where invasive ductal carcinoma (IDC) and ductal carcinoma in situ were found both inside and outside a breast hamartoma. This is the second case reported in the literature.

Case summary: A 51-year-old woman presented with a 6.0 cm breast tumor on mammography and ultrasound, with suspicious areas indicative of malignant transformation. Biopsy of the suspicious area confirmed IDC with intraductal carcinoma. Breast magnetic resonance imaging showed typical hamartoma changes with irregular areas of abnormal enhancement both inside and outside. A breast-conserving surgery was performed, and postoperative pathology confirmed mammary hamartoma, concurrent with IDC and intraductal carcinoma occurring both inside and outside the hamartoma. Subsequently, appropriate adjuvant therapy was initiated. Currently, the patient is in good condition. Breast cancer may be located both inside and outside the ipsilateral mammary hamartoma, which is difficult to detect preoperatively, especially when there is a focus of intraductal carcinoma, requiring accurate assessment of the tumor extent by modern imaging techniques. Early detection of the coexistence of cancer is clinically important as it can alter patient management.

Conclusion: This case emphasizes the importance of modern imaging techniques in accurately evaluating mammary hamartomas associated with malignancies prior to surgery.