To investigate whether low partial pressure of oxygen (Po₂) in prostate cancer (CaP) predicts for biochemical outcome after radiotherapy. We previously reported that hypoxic regions exist in human CaP.

Custom-made Eppendorf Po₂ microelectrodes were used to obtain 100 Po₂ readings from both pathologically involved regions of the prostate (as determined by sextant biopsies) and normal muscle (as an internal control). Fifty-seven patients with localized disease were prospectively studied; all received brachytherapy implants (48 low dose rate and 9 high dose rate) under spinal anesthesia. Nine patients had received prior hormonal therapy. Biochemical failure was defined as two consecutive rises in prostate-specific antigen level, without a return to baseline. Cox proportional hazards regression analysis was used to evaluate the influence of hypoxia on biochemical control, while adjusting for prostate-specific antigen, Gleason score, stage, implant type (low dose rate versus high dose rate), perineural invasion, hemoglobin level, use of hormonal therapy, average (mean) of the median prostate Po₂, average median muscle Po₂, and prostate/muscle Po₂ (P/M) ratio.

With a median follow-up of 19 months (range 4 to 31), 9 patients developed biochemical failure. A threshold analysis of the P/M ratio demonstrated that biochemical control at 2 years differed significantly at a ratio of less than 0.05 versus 0.05 or greater (31% versus 92%, P <0.0001). However, the classic prognosticators were similar in these two groups. On multivariate analysis, the P/M ratio was the only predictor of biochemical control (P = 0.0002).

To our knowledge, this is the first study to correlate the degree of hypoxia in CaP with treatment outcome after radiotherapy. The P/M Po₂ ratio was the strongest predictor for biochemical control on stepwise multivariate analysis. Longer follow up with more patients is planned to confirm this result.