The effect of tumor size and lymph node status on breast carcinoma lethality

It has long been known that both tumor size and the presence of malignant disease in the regional lymph nodes are indicators of outcome for patients with invasive breast carcinoma; however, the way in which these two characteristics could be integrated into an overall assessment of prognosis has not been obvious.

Kaplan-Meier survival estimates (15 years) according to tumor size and lymph node status were obtained for women with invasive breast carcinoma who were observed at the University of Southern California/Van Nuys Breast Center (Van Nuys, California) or at Massachusetts General Hospital (Boston, Massachusetts).

To isolate the individual contributions to death made by tumor size and lymph node status, data were sorted according to both of these variables. For women with tumors of equivalent size, lethality increased with increasing number of positive lymph nodes, such that there was an extra approximately 6% chance of death associated with each positive lymph node. For women with equivalent lymph node status, tumor size was associated with increased lethality, such that each millimeter of tumor diameter was associated with an additional approximately 1% chance of death. The overall lethality was equal to the sum of the contribution from lymph node status and the contribution from tumor size, and this finding led to the creation of a new technique (the Size+Nodes method) for predicting outcome.

The Size+Nodes method was shown to be capable of accurately estimating the risk of death due to invasive breast carcinoma from information on the size of the primary tumor and the number of positive lymph nodes. In addition, this method was used to stratify women into groups according to breast carcinoma lethality. In contrast, classification of women according to lymph node positivity, T status, or disease stage created groups with wide and overlapping levels of lethality.