Growth of metastases from P-388 sarcoma in the rat followig whole body irradiation.

The growth of an allogeneic rapidly growing and metastasizing sarcoma (P-388) in the rat is described. Quantitative and kinetic data are provided concerning the growth of individual metastases produced in three principal regional lymph node drainage groups, and are compared with growth of the primary tumour of origin in muscle; the incidence of pulmonary metastases is also given. The effects on growth of metastases and primaries produced by sublethal whole body irradiation (WBI) before inoculations of 10-10(8) tumour cells are described.Growth of P-388 sarcoma in unirradiated recipients (ED(50) ≃ 5 × 10(3) cells) obeyed the linear growth law proposed by the Mayneord model for tumour growth, but in irradiated recipients (ED(50) < 10 cells) early growth of primaries and metastases approximated more closely to an exponential rate of growth.The ratio M/P of weight of metastases (M) to weight of primary tumour of origin (P) increased at a linear rate with age (t) of tumour, and gave the same slope namely, 0·029 for pelvic node metastases) in unirradiated rats inoculated with a large (10(6)-10(7)) number of cells as in irradiated rats. The slope was decreased to 0·014 for pelvic node metastases in unirradiated rats challenged with fewer (10(4)) cells but not in irradiated recipients. It is postulated that the effects of WBI on growth of metastases are confined to causing a suppression of immunity, and that WBI does not affect tumour spread significantly through other mechanisms.In immunologically competent rats the phenomena of sequestrated progressive growth of isolated metastases in lymph nodes and of a chronic nonprogressive enlargement of nodes in which persistent tumour growth and destruction occurred side by side are described, and effects on prognoses and clinical behaviour, are discussed.The P-388 tumour is considered of value in quantitative and kinetic experimental studies of metastases, and particularly those in which the role of immunity needs to be assessed and measured to avoid confusion with other factors or agents which might affect the spread and growth of metastases.