Influence of secondary inoculum of tumour cells on growth of primary tumour.

The effect of successive inocula of tumour cells given to rats at intervals of 1 to 10 days was examined. If W256 cells were injected on both occasions, the second inoculum failed to grow if given into the footpad as early as 1 day, or intravenously as soon as 4 days, after the first administration. However, although a second inoculum failed to grow, it produced significant augmentation of the growth of the primary implant if given during its latent or growth phases. If the second inoculum contained cells from a fibrosarcoma unrelated to W256, its growth was effectively curtailed if the initial inoculum had preceded it by 24 h or more. However, secondary inocula of fibrosarcoma cells did not augment the growth of the primary W256 tumour.