Effect of external beam radiotherapy on prostatic carcinoma DNA content as measured by static image cytometry

Static image cytometry was used to study the effect of radiotherapy on the DNA content of prostatic carcinoma. Feulgen-stained specimens from 50 patients before and after radiotherapy were examined. The DNA index increased significantly after treatment (p < 0.03), and it occurred equally in those with low (< 1.5) and high (≥1.5) indices. The level of the initial DNA index was significantly related to the rate of symptomatic progression (p < 0.05). The initial change in and final DNA indices were not related to survival however. There was a significant increase in Gleason score (p = 0.001) and histological grade (p = 0.01) after irradiation and, when taken individually, the degree of change was related to survival in both, p = 0.05 and 0.004, respectively. As Gleason score, Mayo grade and clinical stage were not independent variables; none of them was related to survival when corrected for the other factors. Thus, DNA content or ploidy, as well as Mayo grade and Gleason score, increases in recurrent tumor after radiotherapy. This may be of importance when considering what treatment to use and how intensively the patients should be followed up.