Study of the mechanism by which localized preinoculation irradiation enhances the rate of lymphatic spread

KHT sarcoma growing in the foot of C3H mice spontaneously metastasizes to the primary (popliteal) and secondary lymph nodes. Under appropriate conditions, localized preinoculation irradiation of the foot enhances lymphatic metastasis to the primary node. This enhancement could be a result of (1) a decrease in the latent period between inoculation and the initiation of lymphatic metastasis and/or (2) accelerated growth of the primary lymph node. Investigations were conducted to determine which of these factors contribute to the enhancement of lymphatic metastasis. The foot only of C3H mice was either irradiated (2400 rad) or sham-irradiated 1 or 8 days prior to tumor inoculation on Day 0. Each day after tumor inoculation a group of irradiated and sham-irradiated animals had their tumor-bearing foot amputated. The region behind the knee was palpated every 2 or 3 days for the presence of tumor. The period of time (ET50) between inoculation and amputation necessary for 50% of the animals to present with lymphatic metastasis was used to determine the latent period between inoculation and initiation of lymphatic metastasis. The mean time to palpation was used to determine the relative growth rate of the primary lymph node. Localized preinoculation irradiation decreased the ET50 from about 4.9 to 2.7 days. Irradiation also reduced the mean time to node palpation by about 0.9 day for each day amputation was delayed. The results indicated that irradiation both decreased the latent period between tumor inoculation and initiation of metastasis and increased the growth rate of the primary lymph node. The latter is thought to be a consequence of an increase in the rate at which tumor cells were shed into lymphatics