Giving hormone therapy to men while they are getting radiation treatment for prostate cancer may increase their risk of developing a common problem later on, according to new research.

Men receiving both forms of therapy were more than twice as likely to suffer from problems with the rectum (the last part of the large bowel) two years after treatment than were men who received only radiation therapy.

Guiseppi Sanguineti, MD, and colleagues from the National Institute for Cancer Research in Genoa, Italy, reported these findings in the British Journal of Cancer (Vol. 86: 1843-1847).

Radiation therapy is often one of several treatment options for men with prostate cancer. It can be used when the disease has not spread to the lymph nodes or other parts of the body.

As with other forms of treatment, radiation therapy can have serious side effects. About 10% to 20% of men report bowel problems after radiation therapy such as pain, burning, and diarrhea. This is because some of the rectum is exposed to radiation.

Hormone therapy is often used by itself for men whose prostate cancer has spread to the lymph nodes or to distant parts of the body. It can cause prostate cancer cells to stop growing or even to shrink, but it can have its own side effects, including impotence and hot flashes.

Earlier studies have suggested that using hormone therapy as adjuvant treatment in addition to radiation in certain men (those whose cancer has spread, but only locally) may lower the risk that the cancer will return.

While not a cure, hormone therapy can shrink prostate tumors, setting them up to be more easily treated with radiation. It is also sometimes used before radiation, as neoadjuvant treatment.

Hormone therapy also seems to make the cells more sensitive to radiation. While this might help make radiation more effective against cancer cells, it might also affect other healthy cells that receive radiation, such as those in the rectum.

The researchers followed 182 men treated with three-dimensional conformal radiation therapy (3DCRT), which is believed to cause fewer side effects than standard radiation. None of the men's cancer had spread to the lymph nodes.

Eighty-eight of the men received hormone therapy both during radiation and for at least one year after. Ninety-four men were treated with radiation and hormone therapy for less than one year, and some in this group did not receive the hormone treatment at all.

The researchers then asked the men about rectal problems every three to six months. Overall, 36 men developed symptoms such as excess rectal mucus or bleeding that started at least three months after treatment.

The researchers estimated that about one of every five men would have rectal bleeding and other problems within two years after their radiation treatment. The authors said that these problems would affect 30% of men who received hormone treatment for at least one year or more, whereas only 14% of those who received less than one year of hormone treatment would experience these problems.

The study authors suggested that hormone therapy might have been interfering with cells' ability to repair themselves after radiation — a good thing when trying to kill cancer cells, but possibly a bad thing when it comes to normal tissues.

The risk of bowel problems is something that all men considering radiation therapy need to be aware of. However, it's not clear how much this study should factor into a man's decision of whether to get hormone therapy as well.

Only two of the 36 men experiencing bowel problems required surgery.

Meanwhile, experts continue to advise men that the risk of this problem must be weighed against the possible benefit adjuvant hormone therapy may provide in reducing the risk of recurrence, as well as against the risks associated with any treatment for prostate cancer.