A rare case of synchronous bilateral breast cancer with distinct histological subtypes.

BACKGROUND: Synchronous bilateral breast cancer (SBBC) is rare, and the occurrence of distinct histological subtypes in each breast is particularly uncommon, presenting diagnostic and therapeutic challenges. This report describes a case of SBBC with discordant histology in an elderly woman to highlight the diagnostic challenges. CASE PRESENTATION: An 80-year-old woman with no prior breast cancer screening presented with a palpable right breast mass. Imaging revealed bilateral lesions, and core needle biopsy (CNB) confirmed invasive ductal carcinoma (IDC) in the right breast with axillary lymph node involvement. While the initial biopsy of the left breast suggested benign changes, an excisional biopsy was performed due to imaging-pathology discordance, confirming invasive lobular carcinoma (ILC). Immunohistochemistry demonstrated ER and PR positivity, HER2 negativity, and discordant E-cadherin expression, confirming two separate primary tumors. Given the patient's advanced age and comorbidities, she underwent bilateral mastectomy without chemotherapy. Final pathology confirmed IDC (T2N1M0, grade II) in the right breast and multifocal ILC (T2N0M0, grade II) in the left breast. DISCUSSION: This case highlights the diagnostic challenges of SBBC with different histologic types. The limited sensitivity of CNB for ILC underscores the need for close imaging-pathology correlation and excisional biopsy when discordance exists. Management should follow the principles of unilateral disease but be tailored to patient comorbidities and tumor biology. CONCLUSION: SBBC with distinct histological subtypes is rare but clinically significant. Bilateral evaluation and accurate histopathological assessment are essential for optimal outcomes.