The natural history of metastasis of syngeneic murine squamous carcinoma and the prognostic implications of primary tumour size and duration of growth.

A study has been made of the natural history of metastasis of a spontaneous murine squamous carcinoma implanted into syngeneic recipients--a situation where biologically different tumours and variable "host resistance" are not complicating issues. The time distrubution of deaths from metastatic disease was incompatible with a log-normal distribution but was accurately described by an exponential pattern of survival following an initial lag. While the average life of doomed mice correlated with predictions based on growth rates, there was a wide range of survival times indicating random influences on the evolution of metastitic disease. Insofar as tumours which grew to 20 mm3 or less in 5 days after tumour cell injection failed to initiate metastases, while tumours which reached a size of 120 mm3 or greater (irrespective of duration) produced metastases in 38/39 mice, tumour size was a prognostic index. However, within the size range 33-150 mm3 the correlation between metastatic risk and size was not statistically significant. No correlation between metastatic risk and duration of tumour growth from 6 to 29 days was observed. Two integral functions of tumour size and duration were tested but neither gave a better correlation with metastatic risk than did size alone.