The therapeutic response of three human tumor lines maintained in immune-suppressed mice.

Studies were made of the growth and therapeutic response of three lines of human tumor serially transplanted in immune-suppressed mice. They included a well-differentiated colonic carcinoma (HX 13), a poorly differentiated colonic carcinoma (HX 18), and undifferentiated small-cell carcinoma of the bronchus (HX 29). Their histological appearance and growth rates were stable, with volume-doubling times ranging from 6 to 12 days. Studies by the technique of labeled mitoses showed that the growth kinetics of the three tumor lines were very similar, with median intermitotic times in the range of 26 to 35 hr. An analysis of the incidence of single and double takes revealed evidence for variation in susceptibility among the recipient mice. One tumor (HX 18) was transplantable with single-cell suspensions but 10(5) cells were required for 50 percent takes. The response of the tumors to a range of chemotherapeutic agents was studied. There was evidence that drugs that are known to be effective in the treatment of patients did well, in particular 5-fluorouracil against the colonic tumors and cyclophosphamide against the bronchial carcinoma. Long-term regressions induced by cyclophosphamide in the bronchial carcinoma may reflect assistance from host defense mechanisms.