The prognostic value of S-phase fraction in preoperative radiotherapy of rectal cancer

The aim of this study was to analyze the flow cytometric S-phase fraction ( SPF) in rectal tumors before and after preoperative radiotherapy (15x2 Gy) and to compare the findings to the clinical outcome. Archival specimens fro m 84 cases, treated from 1980 to 1988 with S-phase data and complete follow -up were reviewed. There was no significant correlation between SPF and cli nicopathological factors. The median SPF for the 26 diploid tumors before i rradiation was 6.6%+/-3.1, compared to a significantly higher median for th e 58 preirradiated aneuploid tumors (20.3%+/-6.1; p<0.0001). With a median follow-up of 6 years, there was a significant difference in the number of r ecurrences for aneuploid tumors with a pretreatment SPF < and >20.3 (51.7% vs. 20.7%; p=0.029), which also led to a significant difference in recurren ce-free survival (p=0.05). For diploid tumors, a reduction in the percentag e of cells in S-phase after radiation resulted in a borderline significant lower number of recurrences (p=0.06). It is concluded that pretreatment S-p hase measurements may be of predictive value especially for aneuploid tumor s. An alteration in SPF after radiotherapy may also be helpful in predictin g outcome and planning therapy.