Posted on 7 July, 2011
Assessing the outcome of radiation treatment for prostate cancer is both confusing and difficult. The ultimate outcome measure for the treatment of all forms of cancer is the number of people who die from it, but prostate deaths may not occur until ten, fifteen, or more years after treatment. Because the average age of men with prostate cancer who are treated with radiation has traditionally been older than that of men treated with surgery, many will die from other causes before living long enough to ascertain whether or not their prostate cancer would have killed them. In lieu of using death as an outcome measure, most researchers on radiation treatment use a rising PSA level, as do those who measure the outcome of surgical treatment. However, there is a major difference: following surgical removal of the prostate, the PSA level is expected to drop to zero; following radiation treatment, this is not always the case. Radiation is expected to kill all the cancer cells, but not necessarily all the normal prostate cells. The same is true in radiation treatments for cancers of the breast or pituitary gland; radiation is expected to kill all cancer cells but not all normal cells, so the breast and pituitary continue to function after radiation treatments have been completed. Following radiation treatment for prostate cancer, the PSA is expected to fall, but the level of which it is expected to fall is widely debated. Some researchers say it should become less than 1.0, others 0.5, and other 0.3. Assessing the recurrence of cancer following radiation treatment is still more complicated, however, because of what is called the PSA bounce. In approximately one third of men treated with radiation, PSA levels increase one to three years after treatments, then return to a lower level. This rise does not signify the recurrence of cancer but is instead thought to be caused by a delayed release of PSA from irradiated cancer cells. The PSA increase associated with the bounce may last for as long as a year. During this time, there is no way tot ell whether the PSA increase is merely a PSA bounce that has no clinical significance, or whether the PSA increase is merely a PSA bounce that has no clinical significance, or whether it indicates a failure of radiation treatment and a recurrence of the cancer. If it is a PSA bounce, it will go back down; if not, it will continue to rise. Despite the problems in assessing the effectiveness of radiation treatment using the PSA, there is a strong evidence that the lower the PSA goes after radiation, the less are the chances of recurrence. Comparing the outcomes of different studies of radiation treatment also generates problems. Some studies use the ASTRO guidelines, while other studies modify those guidelines or use an absolute PSA nadir, such as 1.0 or 0.5. Statistical problems are abundant: some studies use the actual numbers for the follow up period and other estimate future number based on the follow- up period. |
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