Prostate-specific antigen in the follow-up of prostatic adenocarcinoma treated with external beam radiation

Prostate-specific antigen (PSA) has been shown to be a more sensitive tumor marker than prostatic acid phosphatase (PAP) in prostatic adenocarcinoma: PSA was positive in 54 of our 117 patients (46%) and PAP was positive in 24 (21%). In order to compare the usefulness of these markers during and after radiotherapy serum samples from 24 patients treated with external beam irradiation were analyzed. PAP was only slightly positive in 1 patient (4%) after radiotherapy. His PSA level was highly elevated and he died of progressive disease. In the other 23 patients the cancer was in local control. However, the serum PSA level remained positive in 5 of these patients indicating vital cancer cells may still have been present. An alternative possibility is that metaplastic prostatic cells which secrete PSA were left after radiotherapy, as has been shown to be the case in prostatic hyperplasia. Before radiotherapy increased PSA levels were measured in 3 patients. In 2 of them the level declined to normal within 6 months after radiotherapy. The PAP levels were normal. It is concluded that PSA (positive in 25% of patients after radiotherapy) might be more sensitive than PAP (positive in 4%) in monitoring the effect of radiotherapy in prostatic cancer patients.