Complex sclerosing lesions of the breast mimicking carcinoma: diagnostic pitfalls and the decisive role of immunohistochemistry.

Background: Complex sclerosing lesion (CSL) of the breast is a benign proliferative condition that frequently mimics invasive carcinoma on imaging and in limited biopsy specimens. Radiologic-pathologic discordance may result in diagnostic uncertainty and potentially unnecessary surgical intervention. Accurate pathological assessment, particularly evaluation of myoepithelial cell preservation, is therefore critical to appropriate clinical decision-making. Methods: A retrospective analysis of three female patients diagnosed with CSL at a single medical institution was conducted, along with a focused review of the literature. Clinical presentation, multimodal imaging findings, core-needle biopsy results, histopathological features, immunohistochemical profiles, diagnostic challenges, and subsequent management strategies were systematically evaluated. Results: All three lesions demonstrated imaging features highly suspicious for malignancy on ultrasound, mammography, and magnetic resonance imaging. Core-needle biopsy yielded inconclusive or misleading results, including atypical ductal proliferation and suspected invasive carcinoma, prompting surgical excision. Final pathological examination confirmed CSLs in two patients and breast secretory carcinoma in one patient. Immunohistochemical analysis - particularly the assessment of myoepithelial markers such as p63 and calponin - played a decisive role in distinguishing benign CSL from invasive disease. No recurrence or disease progression was observed during follow-up. Conclusions: CSLs represent a well-recognized diagnostic pitfall in breast practice due to their close resemblance to carcinoma on imaging and in limited biopsy samples. Comprehensive histopathological evaluation, supported by appropriate immunohistochemistry, is essential to establish an accurate diagnosis, guide surgical decision-making, and avoid overtreatment.