Pulmonary metastases of the lewis lung tumor-cell kinetics and response to cyclophosphamide at different sizes.

The response of lung metastases of the Lewis lung tumor to a single dose of cyclophosphamide (300 mg/kg) has been studied as a function of the size of the metastases. Both artificially induced and naturally arising (true) metastases were studied in the absence of a primary tumor. It was found that the artificial metastases exhibited a change in cure probability from 90% to 37% over a size range of a factor of ten. The true metastases had a larger spread in size for a similar change in cure probability but there were large uncertainties in the data and consequently the results are not inconsistent with those for the artificial metastases. Studies of the cell kinetics of the metastases at various sizes in the critical range for curability failed to demonstrate any marked differences. It was concluded that the results of drug treatment could be explained entirely on the basis of an increase in cell number in the larger metastases.