Lobular carcinoma in situ within fibroadenoma: a case report and literature review

Abstract Background: Breast fibroadenoma is the most common tumor with benign biological behavior in women. It is rarely malignant. However, the imaging and clinical features of carcinoma in situ within a fibroadenoma are often similar to those of a fibroadenoma.Case presentation: This study aimed to report the case of a 38-year-old young woman with a regular painless mass in her right breast for 6 years. This tumor had a clear boundary and was composed of epithelial and mesenchymal cells. Most of the area comprised the so-called fibroadenoma structure, besides swelling and proliferation in a small part of the terminal duct and no expression of E-cadherin protein. The histological morphology and immunohistochemistry confirmed the diagnosis of a fibroadenoma with lobular carcinoma in situ. Conclusions: We need to be careful of malignant transformation within fibroadenomas and improve the understanding of lobular carcinoma in situ within fibroadenoma.