Women who were treated for cancer during childhood are about 20 percent less likely to become pregnant than their untreated sisters, according to data from the Childhood Cancer Survivor Study (CCSS).

Risk factors for infertility identified in this study may be useful for pretreatment counseling, the researchers point out in their article published in the Journal of Clinical Oncology.

The CCSS, which is funded by the National Cancer Institute, involves more than 20,000 patients diagnosed with cancer between 1970 and 1986, when they were younger than 21 years old, and who survived at least 5 years.

Dr. Daniel M. Green at St Jude Children's Research Hospital in Memphis, Tennessee, and co-investigators reviewed the records of 5149 female CCSS participants and 1441 sisters who also completed questionnaires between the ages of 15 and 44 years and who were not surgically sterile.

Significant risk factors for reduced fertility that were identified included radiation therapy near the hypothalamus, pituitary, or ovaries and therapy with alkylating agents," particularly lomustine, or cyclophosphamide.

Akylating agents are th likelihood of pregnancy decreased with hypothalamic/pituitary doses greater than 30 Gy. Ovarian/uterine radiation exposure of 5 to 10 Gy was associated with an increase risk of 44 percent, and doses greater than 10 Gy conferred a 72 percent risk.

They also noted that the probability of sterility increased as the dose of the alkylating agent increased.

Green and associates conclude: "These data may be utilized to counsel patients and their parents before initiation of treatment and to identify those at exceptionally high risk for impaired fertility who may benefit from assisted reproduction techniques."