Effect of local hyperthermia on metastases in oral squamous cell carcinoma

In this experimental study, hamsters with oral squamous cell carcinoma (O-1N), which has a high potential for lymph node metastasis, received treatment with local hyperthermia. The effect of hyperthermia on regional lymph node metastases was examined pathologically. O-1N was heated twice, each session consisting of radiofrequency capacitive heating (13.56 MHz) for 40 min at 43 degrees C. Cervical lymph nodes were excised 14, 17, 21, and 28 days after heating and were examined histologically. Hamsters in the sham and control groups were killed on the same days and specimens were examined in a same manner. The incidence of lymph node metastasis was significantly lower in the hyperthermia group (36.4%) than in the sham (68.5%) and control (65.0%) groups (both P=0.02). The patterns of lymph node metastasis in the sham and control groups were more advanced than that in the hyperthermia group. The incidence of lymph node metastasis was very low (7.7%) in hamsters with no evidence of tumour after hyperthermia. On multivariate analysis, hyperthermia correlated with inhibition of cervical lymph node metastasis (P=0.02). Our findings suggest that local hyperthermia inhibits lymph node metastasis when the primary tumour responds histologically to treatment.