Significance of the Tritiated Thymidine Labeling Index in breast cancers.

We carried out studies to determine whether the Tritiated Thymidine Labeling Index (TLI) would correlate with hormone receptors as well as with clinical and histological data. Sixty-four patients with breast cancer were the subjects studied. TLI showed no relationship to age, menopausal status, T-factor, n-factor, stage, or histological type. However, compared to tubule formation, nuclear pleomorphism, and mitotic activity, TLI showed a positive correlation with each and accordingly there was a positive correlation between TLI and Bloom's histological grading. The cumulative disease-free rate at three years was higher in case of a TLI below 4.0 (median TLI value). TLI significantly correlated inversely with the binding sites not only of cytoplasmic estrogen receptors (ERC), but also of cytoplasmic progesterone receptors (PRC) and nuclear estrogen receptors (ERN). Cancers negative for all three receptors indicated the highest TLI, while cancers positive for all three receptors showed the lowest TLI. The results suggest that breast cancers positive for hormone receptors were of low malignancy because lower TLI related to a lower proliferative activity. Thus, TLI is an useful parameter for assessing the clinical status of breast cancers.