Cell cycle changes in ovarian cancer after arabinosylcytosine

Cytokinetic studies were performed using ³H‐thymidine and autoradiographic methods before and after arabinosylcytosine in a patient with ascites due to recurrent ovarian carcinoma. Before Ara‐C, the ascitic fluid had 1900 tumor cells/mm³ the ascitic glucose level was 10 mg%, while after Ara‐C the ascitic tumor cell count was 32/mm³ the ascitic glucose level was 60 mg%. The mean generation time (T_G) was calculated from the median grain count halving time, and the durations of the phases of the cell cycle from the labeled mitoses curves. Before chemotherapy, the flash labeling index (L.I.) was 14%; the mitotic index (M.I.) was 0.4%; T_G = : 180 hrs (total labeled population) and 99 hrs (rapidly proliferating component); S = 62 hrs; G₂ = 6.6 hrs; M = 2.4 hrs; and G₁ = 28 hrs. After Ara‐C the flash L.I. was 40%; M.I. = 1.5%; T_G = 73 hrs (total labeled population) and 45 hrs (rapidly proliferating component); S = 34 hrs; G₂ = 7.0 hrs; M = 1.0 hr; and G₁ = 3 hrs. In this ascitic tumor, when chemotherapy reduced the cell concentration, the remaining viable cells grew more rapidly than the unperturbed cells. The question of whether this phenomenon may have been due to a lowered cell density, increased nutrient supply, or to changes in growth regulatory substances is discussed.