[Biochemical monitoring of prostate cancer treated exclusively by radiotherapy: prognostic value of pretreatment PSA, PSA nadir and PSA half-life].

Objectives: Retrospective evaluation of the prognostic value of pretreatment PSA, PSA nadir and PSA half-life compared to grade and stage after treatment of prostate cancer by radiotherapy.

Patients And Methods: 122 patients (19 T1 (15.6%), 31 T2a (25.4%), 26 T2b (21.3%), 20 T3a (16.4%), 19 T3b (15.6%), 7 Tx (5.7%)) treated by exclusive radiotherapy were studied with a median follow-up of 75.4 months. Treatment consisted of high energy irradiation to the prostate for 31 patients (25.4%) and to the pelvis and prostate for 91 patients (74.6%). PSA was assayed retrospectively. The influence of various parameters on the absence of laboratory failure, defined according to the ASTRO criteria, and on overall survival was studied by univariate and multivariate analysis with a Cox model.

Results: 29.5% of patients did not develop any biochemical recurrence after a mean follow-up of 82 months, while biochemical recurrence occurred in 70.5% of patients after a mean interval of 5 months. Among these patients, 28 (33%) developed clinical recurrence after a mean interval of 26 months (4 to 80 months) leading to death in 17 cases. The modalities of irradiation and pretreatment PSA had no influence on the prognosis. The median PSA nadir of patients without recurrence was 0.24 ng/ml. The recurrence rate was lower for a PSA nadir less than 0.5 ng/ml for biochemical recurrence (45.5% vs 86.8%) (p < 0.0001) and clinical recurrence (9.1% vs 31.6%) (p < 0.05). On multivariate analysis, the PSA nadir (p = 0.009), PSA half-life (p < 0.001) and Gleason score (p = 0.004) were prognostic factors influencing survival, while PSA nadir was the only prognostic factor for biochemical recurrence (p = 0.001). Classification of patients into two groups with a significantly different prognosis according to the presence or absence of at least two favourable prognostic factors (PSA nadir less than 0.5 ng/ml, Gleason score less than 7, PSA half-life greater than 6 months) showed that the 9-year mortality rate was twofold higher in the poor prognosis group than in the good prognosis group (85.5% versus 38.6%).

Conclusion: A nadir PSA level less than 0.5 ng/ml, a PSA half-life greater than 6 months and a Gleason score less than 7 were predictive of a low risk of biochemical recurrence and prolonged survival after treatment by exclusive radiotherapy, in our patients.