Background: Invasive ductal carcinomas of the breast frequently have an intraductal (in situ) component at the tumor periphery that, in some cases, is included in the measurement of the tumor and thereby increases the size of the tumor beyond that of the invasive component.
Methods: Thirty-seven ductal carcinomas containing intraductal and invasive components were analyzed. The total tumor size, the size of the invasive component, the percentage of intraductal component, and the estimated tumor volume were assessed for each tumor.
Results: The mean size of the invasive component was 6.5 mm in axillary lymph node negative patients and 14.3 mm in those with axillary lymph node metastasis (P = 0.0001). The mean total tumor size was 13.7 mm and 17.6 mm (P = 0.035) and the mean percent of intraductal component was 52% and 26% (P = 0.015) in patients with negative and positive axillary lymph nodes, respectively. Ninety-two and four tenths percent of the difference in mean estimated total tumor volume between patients with negative and positive axillary lymph nodes was attributable to the difference in the volume of the invasive component alone.
Conclusions: In small ductal carcinomas of the breast, the size of only the invasive component, as determined by microscopic measurement, is a better predictor of axillary lymph node status than is the total tumor size. The well established prognostic value of total tumor size largely is due to its reflection of the size of the invasive component.