Tumor size is an unreliable predictor of prognosis in basal-like breast cancers and does not correlate closely with lymph node status.

Larger breast tumors tend to be associated with a greater number of axillary lymph nodes involved with metastatic tumor than are smaller tumors. This rule may not fully apply in BRCA1-related breast cancers. We hypothesized that the rule also might not apply in basal-like breast cancers (BLBC), and further, that disruption of this relationship would impact on prognosis. In 1,324 non-BLBC (87.1% of 1520 tumors), after adjustment for grade, a strongly positive correlation between increasing tumor size and increasing number of lymph nodes involved by tumor was observed (P for trend <.001). The correlation was much weaker in 196 BLBC (12.9%) (P for trend = 0.58). Similarly, a worsening breast cancer-specific survival with increasing tumor size was observed in non-BLBC (P for trend <.001) but not in BLBC (P for trend = 0.43). The "size-nodes" relationship in BLBC is distinct and is similar to that seen in BRCA1-related breast cancer, further suggesting biological similarities between these sub-types of breast cancer. Moreover, tumor size is not a strong indicator of prognosis in BLBC.