Women who received radiation to treat Wilms tumor, a childhood kidney cancer, are at increased risk of complications during pregnancy and should be carefully monitored by their doctors, according to a study in the Journal of Clinical Oncology (Vol. 20, No. 10: 2506-2513).

However, those women should not be afraid to get pregnant, experts said.

According to the American Cancer Society (ACS), about 400 new cases of Wilms tumors are found each year in the US, accounting for about 6% of all childhood cancers. The overall survival rate is about 92%.

Treatment for Wilms tumor, usually requires surgery to remove a kidney. Patients may then be treated with chemotherapy or radiation, or both.

Researchers focused on pregnancy outcome in a study that was the largest of its kind. They used questionnaires and medical records of 309 patients with births who enrolled in the National Wilms Tumor Study Group. The study included men and women who had had the disease as children.

The authors found that the partners of male survivors of Wilms tumor did not have increased pregnancy complications. But female survivors of Wilms tumor who were treated with radiation had a higher risk for early or threatened labor.

Also, their children were more likely to be premature (less than 36 weeks gestation), and to have increased risk of congenital defects such as cleft lip and palate, or undescended testes.

"The trend we saw suggests that lower dose radiation is not as bad as higher dose radiation," said Daniel Green, MD, lead author and researcher at Roswell Park Cancer Institute in Buffalo, N.Y. "But we don't know that there's a dose that has zero risk. So all of these women should be treated as though they are high risk pregnancies."

Green says radiation therapy can stop growth of bone and damage soft tissues.

"The uterus is a soft tissue, so sometimes the part that's included in the radiation area is much less elastic and much less able to change shape and size (during pregnancy)," he said.

"Any woman who's had radiation that included her pelvis should be followed by an obstetrician who's experienced in high risk pregnancy management. Usually that's at a major medical center," Green said. He said women should get a copy of their radiation therapy records to bring to the obstetrician.

While the women have a greater risk of complications, it is not enough that doctors would tell the women to avoid pregnancy.

"I've talked to some of my own patients and they'll say they don't want to get pregnant because they're afraid of what the outcome is going to be or afraid that their kid is going to have cancer," Green said. Studies to this point say women do not need to worry, Green said.

ACS spokesperson Teresa Vietti, MD, agreed.

"I think they should be monitored more closely," said Vietti, a pediatric cancer specialist at the Washington University School of Medicine in St. Louis and member of the ACS editorial board.

Vietti said, "I don't think that it should scare them away from pregnancy."

One missing piece of the puzzle involves the fertility of women who survived Wilms tumor, Vietti noted.

"One of the things this study didn't have is how many women wanted to get pregnant but didn't and were actually sterilized by the radiation therapy," she said.

Green estimated it will take another year to complete an analysis of Wilms tumor survivors' fertility. He agreed that it's a concern.

"Usually these are pretty precious pregnancies to these women because a lot of them don't know if they can get pregnant at all," he said.