Growth rate, kinetics of tumor cell proliferation and long-term outcome in human breast cancer.

Thymidine labelling index (LI) was prospectively assayed in vitro in a series of 128 consecutive patients with breast cancer. The follow-up was longer than 15 years for all patients. The distribution of LI was log normal and patients were subdivided into 3 groups (patients with LI = m +/- sigma, lower than m - sigma and greater than m + sigma where m is the geometrical mean). The incidence of relapse and death remained significantly lower in the group with a low LI than in the 2 other groups, whereas the difference between the 2 other groups faded away when follow-up exceeded 10 years. Multivariate analyses show that LI is one of the two most important independent prognostic indicators for relapse or death, the other being histological grading. Data concerning 2,648 patients treated at our Institute, prior to the introduction of chemotherapy into treatment protocols, have been used to investigate the influence of tumor growth rate on the probability of distant dissemination. A model of the natural history was used, in order to generate metastasis appearance curves, in 3 subgroups of patients, according to the value of the tumor doubling time (TDT). Our results show that after a follow-up exceeding 8 years, there is no longer any difference between the subgroups of patients with rapid or intermediate growth rate, whereas after 25 years large and highly significant differences in relapse and survival between the slow-growing tumors and the other two subgroups still remain. These two sets of data concur to show that tumor growth rate or proliferation rate correlates with the probability of metastatic dissemination.