ORLANDO—Radiotherapy for rectal cancer decreases subsequent clinical detection of prostate cancer, researchers report.
Using the Surveillance Epidemiology and End Results (SEER) database, Karen E. Hoffman, MD, and her colleagues at Massachusetts General Hospital in Boston identified 1,574 men with local or regional rectal cancer treated in 1988-1997 with external beam radiotherapy (EBRT) and sphincter sparing surgery (SSS).
The researchers say they chose this period to include men potentially screened for prostate cancer in the PSA era and to allow for a minimum of six years after rectal cancer for detection of subsequent prostate cancer. SSS permits digital rectal examination of the prostate.
Prostate cancer was diagnosed in 20 men, 72% fewer cases than would be expected in the general population of similar age and race. The researchers compared these men with 3,125 men with local or regional rectal cancer treated with SSS but not EBRT and 24,578 men with local or regional colon cancer not treated with EBRT. Prostate cancer was diagnosed in these two groups of men who did not receive EBRT at a rate similar to that of the general population.
The investigators, who reported their findings here at the third annual Prostate Cancer Symposium, speculate that PSA testing may be less sensitive in men treated for rectal cancer with EBRT, and study findings may reflect delays in prostate cancer diagnosis.
Another possible explanation for the decrease in clinically detected prostate cancer is that EBRT for rectal cancer may treat subclinical prostate cancer or impede prostate cancer development by altering the hormonal or stromal milieu.