Tumor size and survival in multicentric and multifocal breast cancer.

PURPOSE Current AJCC/UICC staging of early breast cancer defines tumor stage using the largest focus, adding the suffix "(m)" to indicate multiplicity. This method may underestimate the total tumor burden in multifocal and multicentric breast cancer (MMBC). This study examines other measures of tumor size in MMBC to determine which provides the best fit in a multivariate model for survival outcomes. PATIENTS AND METHODS This prospective cohort study used data from the Australian Capital Territory and New South Wales Breast Cancer Treatment Group database to identify 812 women with ipsilateral invasive breast cancer; 141 of these women had MMBC. The pathology slides of all women with MMBC were reviewed and all foci of invasive breast cancer were re-measured. The measures of interest were the diameter of the largest deposit, the aggregate diameter and the aggregate volume. These measures of tumor size were included with other clinicopathological features of MMBC in a multivariate analysis to assess their relationship with progression-free survival (PFS) and overall survival (OS). RESULTS Tumor size was associated with PFS and OS in MMBC using any of the three measures; however, the diameter of the largest deposit provided the best fit in the multivariate model for OS. CONCLUSION Tumor size is an important prognostic factor for MMBC, and the diameter of the largest deposit provides a better fit in a multivariate model for OS than aggregate diameter and aggregate volume. Therefore, tumor size in MMBC should continue to be measured using the diameter of the largest deposit.