Lymphatic metastasis from tumors transplanted into the pre-irradiated footpad of the rat.

BACKGROUND

In the literature there is some evidence that the incidence of metastases may increase after radiation treatment.

METHODS

In order to investigate whether radiation-induced changes in the lymphatic drainage may alter the rate of lymph node metastasis, the center part of the left hind foot of rats was irradiated with a dose of 1 x 55 Gy before inoculation of tumor cells into the irradiated part of the footpad at different time intervals. Cells of 2 different tumor lines were employed. A rarely metastasising rhabdomyosarcoma, R-1, to look for a possible enhancement of lymphatic metastases, and a readily metastasising mammary carcinoma, Cl-2, in case of a possible decrease in the rate of lymphatic metastasis from tumors growing in pre-irradiated footpads.

RESULTS

The incidence of regional lymph node metastasis decreased for R-1 tumors growing in pre-irradiated footpads, but not for Cl-2 tumors. Furthermore, the average time required for lymph node metastasis to attain a reference volume of 100 mm3 is not significantly influenced by pre-irradiation of the footpad. No difference was observed in average times for doubling in volume of lymph node metastases originating from primary tumors in pre-irradiated footpads. Abscopal effects after footpad irradiation may cause a 50-fold increase in size of regional lymph nodes and, therefore, histological examination is essential for verification of lymph node metastases.

CONCLUSIONS

Damage to the lymphatic system to be expected in the irradiated footpad did not enhance the incidence of regional metastasis of R-1 tumors. A reduced rate of lymphatic metastasis contradicts earlier findings of enhanced lymphatic metastasis development of R-1 tumors, growing in pre-irradiated gastrocnemius muscles. The influence of irradiation on regional metastasis formation seems to be "tumor bed" dependent for R-1 tumors.