A new retrospective study has reported that the number of tumor foci influences breast cancer prognosis and should be considered in staging breast cancer. The authors compared recurrence and survival patterns of multicentric/multifocal breast cancer compared to unifocal disease. TNM (tumor-node-metastasis) breast cancer staging has been considered standard for more than 50 years. In multicentric and multifocal tumors, T (tumor size) is defined as the size of the largest tumor. Multifocal tumors are not considered multiple tumors (multiple primary malignancies); they originate from a unique cell and grow multifocally. Multicentric tumors develop simultaneously, but not from a single cell. Normally, no attempt is made to determine whether the disease is multifocal or multicentric when multiple foci are discovered in breast cancer.

The study included a series of breast cancer patients diagnosed between 1963 and 2007. Patients were assigned to two comparable groups of 288, based on whether they had multifocal/multicentric or single tumors. Patients in the two groups were matched according to tumor size, grading, and hormone receptor status. Disease free survival and occurrence of local relapse or of metastatic disease were determined.

The average breast cancer-specific survival time was 203.3 months in the multicentric/multifocal group, compared with 221.6 months in the group with single tumors. Local relapse and distant metastasis was found to be more prevalent in the multifocal group. Focality and centricity were found to predict overall survival, local relapse and distant metastasis. Tumor size, histopathological grading, hormone receptor status, and lymph node status all are well-established prognostic indicators. The authors conclude that the number of foci, which is currently not reflected in the TNM classification, should be considered as an independent prognostic factor.