Mitotic Circadian Rhythm in a Fast-Growing and a Slow-Growing Hepatoma: Mitotic

5UMMARY-A circadian rhythm is reported in the mitotic activity of a fast-growing hepatoma (5S1 K) and a slow-growing hepatoma (SS1 H). These tumors a,e 2 different sublines of a spontaneous hepatoma transplanted in 1949 by j. W. Wilson, Brown University, Providence, Rhode Island, into C3H/StWi strain. 5igniAcantly higher values in mitotic activity were observed during light periods than during dark periods. The SS1 Khepatoma presented higher values than the SS1 H hepatoma during the dark period, but thevalues for both hepatomas were not different during the light period. The variation was signiAcantly higher in the slow-growing hepatoma and approached that of the immature liver.- j Nat Cancer Inst 44: 581-585, 1970. MITOTIC circadian rhythms in tumors have been investigated, with different results reported (1, 2). A mitotic circadian rhythm in a mammary carcinoma was reported some years ago, and it