The incidence of lung metastases in C3H mice after treatment of implanted solid tumours with x-rays or surgery.

C3H mice were implanted with pieces of spontaneous mammary carcinoma which were irradiated or removed surgically when they had grown to 6·5 mm mean diameter. The incidence of lung metastases was determined from samples taken at various times up to 6 months later. Single x-ray doses and fractionated schedules up to 15 fractions in 18 days were used, no significant difference being observed in the results for all these schedules.On the major question of whether radiation caused an increase in the number of lung metastases the study is inconclusive. The incidence of metastases was found to be 8% if the implanted tumour was cured by the radiation, whereas if the radiotherapy did not cure the tumours the incidence was 35%. This difference between the two groups was significant. If tumours recurred locally after radiotherapy and were then removed surgically, the incidence of lung metastases was significantly greater than that after surgery of unirradiated tumours. The incidence of metastases was similar after curative surgery and after curative radiotherapy.