Cell population kinetics of fast- and slow-growing transplantable tumors derived from spontaneous mammary tumors of the DBA/2 Ha-DD mouse.

The proliferation kinetics of a fast-growing apontaneous mouse mammary tumor subline (SMT-F) and a low-growing spontaneous mouse mammary tumor subline (SMT-S) tumor have been determined autoradiographically at 2 different stages of tumor grwoth. The length of the cell cycle and the growth fraction for SMT-F were 11.2 hr and 0.85, respectively, on Day 14 and 12.1 hr and 0.78 on Day 28. For SMT-S these same parameters were 15.6 hr and 0.50 on Day 14 and 16.1 hr and 0.45 on Day 28. On Days 14 and 28 the mitotic indices were 1.3 and 1.0%, respectively, for SMT-S, compared to 2.2 and 1.9% for SMT-F. The cell loss rate, cell loss factor, and cell loss were significantly higher for SMT-F than for SMT-S. The difference in the growth rates for these 2 tumro lines was attributable to a slight prolongation of the lenght of the cell cycle and a reduction in the growth fraction of SMT-S.