Supplementary Material for: Synchronous Bilateral Breast Cancer with Heterogeneous Histology: Invasive Ductal and Lobular Carcinoma

Background: Synchronous bilateral breast cancer (SBBC) is rare, comprising 2–5% of all breast cancer cases. Even more uncommon is the presence of discordant histologies in each breast. This report discusses a case involving invasive ductal carcinoma (IDC) in the left breast and invasive lobular carcinoma (ILC) in the right breast. Case presentation: A 46-year-old Arab woman presented with a six-month history of a growing lump in the left breast and a newly noticed nodule in the right breast. Imaging and biopsy confirmed IDC (Grade 2, ER+/PR+/HER2–) in the left breast and ILC with LCIS in the right breast. Bilateral axillary lymphadenopathy was observed. She underwent neoadjuvant chemotherapy (doxorubicin/cyclophosphamide followed by paclitaxel), followed by a left radical mastectomy with axillary dissection. Hormonal therapy (goserelin and exemestane) and adjuvant radiotherapy were initiated. Right breast surgery is pending. Conclusion: SBBC with discordant histology necessitates a multidisciplinary, individualized treatment approach. Hormone receptor status, tumor biology, and extent of disease all influence treatment decisions. This rare clinical scenario highlights the need for further research and specific management guidelines.