"Multiple biases and the small number of patients studied earlier render the conclusions premature, necessitating further research," explained Dr. Jeanne Petrek, a breast surgeon at Memorial Sloan-Kettering Cancer Center. She co- authored the paper, which was published in the April 1st issue of the journal Cancer.
"We are not saying that it's unsafe to become pregnant after surviving breast cancer," Dr. Petrek stresses. "What we are saying is that the existing studies examining this issue are inconclusive and that more research is needed."
The researchers point out that the previous studies were retrospective, containing data gathered from hospital records where subsequent pregnancy was not recorded. Therefore, the reported data were dependent on the memory of the treating physician. This method predisposed the studies to a "recollection bias," which may account for the good outcomes reported.
In addition, the researchers also evaluated studies that reported better medical outcomes for breast-cancer patients who became pregnant after treatment than for matched controls who did not. However, the reviewers contend that these results may be flawed because the dates of disease recurrence were not taken into account. Therefore, the overall health of both groups is not accounted for accurately, rendering the comparison unreliable.
In light of laboratory data that have demonstrated the influence of estrogens on the promotion of breast cancer, the investigators say that further research is needed to determine if tumor growth is accelerated in pregnant women. "Tumor growth could occur because the total estrogen levels are vastly higher during pregnancy than at any other time in an adult woman's life, and the proportion of the estrogens are different," Dr. Petrek explains. "We simply do not know what effect this will have on the breast-cancer survivor."
Other Childbearing Issues Also Need Study
The researchers also emphasize the need to address other reproductive health concerns facing young breast-cancer survivors. These include treatment side effects, such as the risk of infertility and premature menopause, and alternatives such as in vitro fertilization, adoption, and surrogacy. "For the younger woman with breast cancer, these issues are of paramount importance," says Dr. Antonella Surbone, an Associate Attending Physician at Memorial Sloan- Kettering Cancer Center and co-author of the paper. "Clinicians must thoroughly discuss the risks associated with treatment and other childbearing issues and alternatives with their patients both before and after treatment."
This summer, Memorial Sloan-Kettering Cancer Center will launch the first prospective trial to study a host of complex childbearing issues facing young breast-cancer survivors. Especially designed questionnaires will be used to collect data on menstruation, pregnancy, the effect of chemotherapy on the reproductive system, and the quality-of-life issues facing women who become infertile after high-dose regimens of chemotherapy.
"Only a carefully designed prospective study will resolve the uncertainties surrounding the many issues of reproduction in women who have been treated for breast cancer," adds Dr. Surbone.
Memorial Sloan-Kettering is the world's oldest and largest private institution devoted to prevention, patient care, research and education in cancer. Throughout it's long and distinguished history, Memorial Sloan-Kettering has played a leadership role in defining the standard of care for persons with cancer. In 1996, Memorial Sloan-Kettering was named the nation's best cancer center by U.S. News and World Report for the fourth year in a row.