This study investigated if measuring the levels of prostate specific antigen (PSA) after cancer therapy could indicate a cure or if the patient should be considered for long term androgen deprivation (suppression) therapy. The main finding was that lower PSA blood levels predict better survival in patients with prostate cancer.

Male hormones (androgens, the most common of which is testosterone) fuel the growth of prostate cancer. Treatments that decrease the body's levels of androgens (called androgen deprivation therapy or ADT) decrease the size and slow the growth of prostate cancer. However, long term androgen suppression has been linked to side effects related to the lowered levels of male hormones, such as sexual dysfunction.

Data from 734 men with cancer confined to the prostate gland (localized) and cancer which has spread beyond the prostate but did not reach distant parts of the body (locally advanced prostate cancer) was analyzed. 371 men received radiotherapy alone, and 363 received combined ADT and radiotherapy treatment for 6 months. PSA levels (a marker for prostate disease) were measured at the start and then every 3 months for 2 years, then every 4-5 months up to 5 years; thereafter once a year. The investigators expected patients to obtain a PSA end value of 0.5ng/ml at the end of the 6 months treatment, or for this low PSA level to be reached at some point during the 8 year follow up period (PSA nadir).

Results showed that patients who received radiotherapy alone had less chance of reaching a PSA level below 0.5ng/ml compared to those who received the combined treatment. The study also showed that when the PSA end value was greater than 0.5ng/ml, 20% of men died of prostate cancer during the 8 year follow up in the radiotherapy group, and 16% in the combined treatment group. When the PSA end was lower than 0.5ng/ml, deaths during the 8 year follow up period were reduced to 4% in the radiotherapy group and 7% in the combined treatment group.

In summary, this study shows that patients are more likely to survive prostate cancer if they have a PSA level of less than 0.5ng/ml following 6 months of treatment. Those that do not reach this low PSA level should be put forward for or recommended long term androgen suppression therapy.

The main limitation of this study is that the authors evaluated only one method of androgen suppression therapy [luteinising hormone releasing hormone (LHRH) agonist and an anti-androgen] and did not provide any details on this treatment.