Changes in cell kinetics induced by primary chemotherapy in breast cancer.

Changes in the 3H-thymidine labelling index (3H-TdR LI) of primary tumor induced by cytoreductive chemotherapy were evaluated in 26 patients with locally advanced breast cancer subjected to mastectomy after different systemic therapies. A significant reduction of 3H-TdR LI by primary chemotherapy was observed in 11 cases. Changes in cell kinetics were related to the pretreatment proliferative activity: significant increases were observed in 70% of tumors with a very low 3H-TdR LI (less than 25%) and significant decreases in 100% of tumors with a very high 3H-TdR LI (greater than 7.0%). There was no correlation between pretreatment 3H-TdR LI and the objective clinical response, which was conversely related to posttreatment cell kinetics. The 2-year progression rate was lower for patients whose residual tumors after treatment had remained (2/7) or become (1/8) slowly proliferating than for patients whose tumors had remained (5/7) or become (4/4) rapidly proliferating.