Prediction of early course of breast carcinoma by thymidine labeling

The thymidine labeling index (TLI) was measured in vitro in 278 primary breast carcinomas. In 227 operable women treated by radical mastectomy, TLI's below the median of 4.55% carried a probability of relapse of 20% at four years, in contrast to 52% for TLI's above the median (P = 0.0001). The probability of relapse was significantly related to the TLI independent of TNM pathologic stage, axillary lymph nodal status alone, estrogen receptor (ER) content, or menopausal status. The abilities of the TLI and nodal status to predict early relapse were equally strong and independent, whereas other variables tested had less or no independent predictive capacity. The predictive value of the ER content depended largely on its relationship to the TLI, and ER was related to the probability of relapse in the below median TLI group only. The TLI can select a subgroup of node‐negative patients with a relapse‐expectancy of approximately 50% at four years.