Is Single or Multiple Breast Cancer More Common?

Breast cancer most commonly presents as a solitary (unifocal) lesion—meaning a single tumor focus within the breast. Unifocal disease accounts for approximately 70–85% of newly diagnosed invasive breast cancers. In contrast, multifocal breast cancer—defined as two or more distinct tumor foci within the same breast quadrant, all sharing the same histologic subtype and clonal origin—is observed in roughly 5–15% of cases. Multicentric disease—characterized by separate tumor foci in different quadrants of the same breast—is less common, occurring in about 2–8% of patients.

The distinction between unifocal, multifocal, and multicentric disease carries important clinical implications. Accurate preoperative imaging—including diagnostic mammography, targeted ultrasound, and often breast MRI—is essential to detect additional foci that may not be apparent on physical exam or conventional imaging alone. Underestimation of multifocality or multicentricity can influence surgical planning, potentially leading to positive margins or the need for re-excision after lumpectomy.

Pathologic evaluation remains the gold standard for confirming multifocality, particularly when multiple lesions are identified on imaging. Histologic concordance—including similar receptor status (ER, PR, HER2), grade, and molecular features—supports a clonal relationship and informs decisions regarding local therapy and systemic treatment strategies.