PSA Monitoring after Treatment
After treatment for prostate cancer the PSA level should decrease.
Following radical prostatectomy, the PSA level should fall to a non-detectable level (<.05ng/mL) within 12 weeks providing successful removal of all cancer and benign prostatic tissue has been achieved. Following surgery the PSA level is checked at three months and then every six months for the first two years and thereafter annually. If the PSA becomes detectable again after surgery this usually indicates that there is residual prostate cancer present. This cancer may be at the site of prostate removal (prostate bed), termed a local recurrence; outside of the prostatic bed in lymph nodes or bones (termed a systemic recurrence); or both a local and systemic recurrence. Determination of whether the relapse is just local or systemic is difficult. The likelihood of either scenario can be estimated by looking at the pattern of PSA recurrence (i.e. an early and rapid PSA recurrence tends to suggest a systemic relapse) in conjunction with knowledge gained about the cancer from the removed prostate gland and lymph nodes (if removed). Recently, a super sensitive scan for prostate cancer has been developed. This is called the Gallium PSMA (Prostate Specific Membrane Antigen) scan. The PSMA scan is useful in helping to determine where a recurrence may have occurred. Currently PSMA scans are available at Mercy Radiology in Auckland and are not presently funded by Southern Cross . If the relapse is thought to be local only then consideration may be given to delivering a course of radiotherapy to the prostate bed to eliminate the remaining cancer cells.
Following radiation therapy (external beam or seed brachytherapy) the fall in PSA is far slower than that following surgery. Usually the PSA takes at least eighteen months to reach its lowest point. The PSA will always be detectable following radiotherapy and there may be transient PSA elevations (PSA bounce) in the first few years following radiotherapy. The lower the level of PSA that is achieved the lower the chance of future disease relapse.
Castration refers to the therapeutic reduction of a mans testosterone level to nearly zero. Testosterone is produced by the testicles, the adrenal glands and also by the cancer cells themselves. The presence of testosterone is critical for the continued growth of prostate cancer. Castration results in temporary remission of prostate cancer and is standard treatment for men with metastatic prostate cancer. In recent years research has shown that chemotherapy with Docetaxel may also extend survival in men newly diagnosed with metastatic prostate cancer.
Castrate levels of testosterone can be achieved in one of two ways:
- Surgical removal of the testicles.
- Injection of a drug every 1-6 months.
Following castration the PSA level often falls rapidly. The ultimate level that the PSA reaches is predictive of the future behaviour of the cancer. After several years the cancer may begin to grow and produce more PSA in spite of castrate levels of testosterone; this is termed castrate resistant prostate cancer (CRPC). The development of CRPC indicates that symptoms from the cancer are likely to arise and that the overall prognosis from the disease is less favourable. There are several new drugs (Abiraterone/Zytiga, Enzalutamide, Radium 223, Docetaxel) which have been proven to extend survival in men with CRPC.
Temporary suppression of testosterone levels prior to, during, and after radiotherapy is also commonly performed. This improves the chance of cure of the cancer with radiotherapy.