[Circadian-rhythm of tumor growth in non-vascularized tumor]

Circadian-Rhythms of tumor growth rates of Walker-256 implanted in the dorsum side of hind paw of Wistar rats (Male 5-6 weeks age) were observed. Tumor size was measured at 7 A.M. and 7 P.M. The tumor growth rate was determined by the following method. Rday = T (P.M.)/T (A.M.). Rnight = T (A.M.)/T (previous P.M.). Rday and Rnight: Tumor growth rate during day and night, respectively. T: Tumor size. The tumor growth rate, for those less than 750 mm3 in size and in which tumor vessels did not form yet, was 0.10 +/- 0.5 on Rday, 0.29 +/- 0.12 on Rnight (p less than 0.05). Tumors of more than 1,500 mm3 forming tumor vessels did not show a significant difference in the degree of the tumor growth rate (Rday: 0.14 +/- 0.07; Rnight: 0.212 +/- 0.05) (p greater than 0.05). Tumors in which vessels were injured and showed microvascular disturbance due to MMC (A. i) or thermochemotherapy using warmed physiological saline injected into tumor vessels after chemotherapy, were damaged on Rday and enhanced on Rnight for 3-7 days after these kinds of treatment. The tumor in unformed tumor vessels or damaged types showed, rapid size increase at night. Therefore, the Circadian-Rhythm tumor vessels in microtumor or damaged tumor may be treated with antimetabolic agents such as 5-FU at night for inhibition of microtumor or micrometastatic tumor.