Histologic heterogeneity in synchronous bilateral breast cancer: a case report and literature review

Synchronous bilateral primary breast cancer (sBPBC) accounts for 2.9%-3.9% of newly diagnosed breast cancers, while cases with discordant histologic subtypes are exceptionally rare. We report on a 59-year-old woman with synchronous left-sided invasive ductal carcinoma (IDC) and right-sided invasive lobular carcinoma (ILC). The patient underwent bilateral breast-conserving surgery with sentinel lymph node biopsy, followed by adjuvant radiotherapy and endocrine therapy. No recurrence or metastasis was observed during the 12-month follow-up. To place the present case in the context of the existing literature, we comparatively reviewed seven previously reported cases of synchronous bilateral IDC and ILC. The comparison illustrated considerable heterogeneity in the clinicopathological characteristics, molecular profiles, nodal involvement, treatment strategies, and clinical outcomes. These findings support independent characterization of each breast lesion and individualized treatment planning based on the features of both tumors.