Synchronous bilateral breast malignancies: Diagnostic implications of histologic diversity

A 75-year-old woman presented with a palpable left breast mass and was subsequently diagnosed with synchronous bilateral breast cancer (SBBC). Imaging revealed multiple suspicious lesions in both breasts, prompting targeted biopsies. Histopathology revealed three distinct tumor types: ductal carcinoma in situ (DCIS) in the right breast; encapsulated papillary carcinoma and invasive lobular carcinoma (ILC) in the left breast—all ER/PR positive and HER2-negative. This histologic diversity is unusual, as SBBC typically shares the same tumor histology. The patient underwent bilateral mastectomy with negative sentinel lymph node biopsies. Given the absence of high-risk tumor features (e.g., triple-negative or HER2-positive status), neoadjuvant therapy was not indicated. This case highlights the diagnostic importance of imaging in identifying target lesions and the necessity of biopsying multiple suspicious areas to determine tumor heterogeneity. Management decisions in SBBC must be individualized based on the most aggressive tumor. Early detection and comprehensive bilateral assessment are critical for optimal patient outcomes in cases with multifocal and histologically diverse disease.