The in vitro sensitivity to hyperthermia and radiation of esophageal cancer cells obtained from 50 patients was assayed by using the in vitro succinate dehydrogenase inhibition test, and the findings were correlated with data on DNA analysis. The DNA distribution patterns were grouped into types I, II, III and IV, according to the frequency of aneuploid cell populations. Esophageal cancer cells of high ploidy (type IV) had a lower sensitivity to radiation, however, a greater sensitivity to hyperthermia as compared to cells of low ploidy (type II). The sensitivity to hyperthermia was determined as positive in 2 of 8 for type II, in 7 of 25 for type III, and in 9 of 17 for type IV. In contrast, the positive sensitivity rates to radiation in type II, III, and IV were 25.0, 8.0, and 5.9%, respectively. When cells were exposed to combination of radiation with hyperthermia, the positive sensitivity rates increased in all groups (50.0, 44.0 and 70.6% in type II, III, and IV, respectively). There was a significant correlation between mean DNA values and the SD activities following exposure to heat treatment or radiation. These data, describing that cancer cells of high ploidy might have greater sensitivity to hyperthermia compared to radiation, indicate the clinical benefits of hyperthermia in cases of esophageal carcinoma, especially for patients with high DNA ploidy.
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