Differences in chemosensitivity between subcutaneous and pulmonary tumours

The response of a murine tumour to cyclophosphamide has been studied in two sites (subcutis and lungs) over a wide range of tumour sizes. The site of tumour growth has been shown to have a marked influence on chemosensitivity for tumours of equivalent size. Pulmonary metastases are much more sensitive than subcutaneous implants. In the lung there is a simple decrease in curability as the tumour grows, presumably reflecting the increase in clonogenic cells per tumour. In the subcutis the pattern is more complex. An initial sensitivity is followed by a decline during the avascular phase of growth. As the vascular network develops the tumours regain their chemosensitivity. There is no correlation between volume doubling time and chemosensitivity. This study indicates that it is impossible to predict the response of pulmonary deposits from a study of subcutaneous implants.