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30 May 2005
New Egg Freezing Technique May Help Cancer Sufferers 
Researchers at the University of Michigan (U-M) Comprehensive Cancer Center say a new egg freezing technique might allow women diagnosed with cancer the opportunity to have children when cancer treatments rob them of their fertility. By having her eggs frozen before she begins cancer treatments, a woman can preserve the hope of one day having a baby. But freezing eggs is the easy part; thawing them safely is the challenge. Efforts to freeze a woman's eggs, or oocytes, in the past have not worked well because the cells are large. When the egg is thawed, ice crystals cause ruptures that prevent the egg from being fertilized. To tackle the freezing problem, U-M researchers looked beyond traditional techniques to a method called vitrification. This cryopreservation technique allows the eggs to be cooled fast enough that the transformation from liquid to solid is instantaneous. No ice crystals form and the consistency resembles a viscous glassy state. Research so far has used mouse oocytes but U-M expects to make the technology available in the clinic soon. "With traditional slow-freeze techniques, just over half the eggs survive the thawing process. Using vitrification, we are getting 98 percent survival. For a woman with cancer, these are the only eggs she's ever going to have, so it's important that as many as possible remain viable," says Gary D. Smith, director of the Fertility Counseling at the U-M Comprehensive Cancer Center. Smith's results were presented at the World Congress on In Vitro Fertilization, Assisted Reproduction and Genetics in Istanbul. But the new method is not without its complications. When eggs are warmed after vitrification, fertilization rates with conventional IVF are low. Researchers have found that a single sperm cell must be injected into a single oocyte, a technique called intracytoplasmic sperm injection, or ICSI. While ICSI is an established technique used in assisted reproduction, it is more complex and costs more than traditional methods. Using mouse oocytes, 80 percent of eggs that had been vitrified became fertilized with ICSI, with a live birth rate of about 30 percent, comparable to conventional IVF when eggs are not frozen. For egg freezing to work, it must be a mature oocyte, which means a woman must have 14 days of hormone treatments to stimulate mature egg production. This could limit its applications for some women, especially for those with cancers fueled by estrogen, such as breast cancer. In addition, the hormone treatments require delaying the start of cancer therapy, which may not be an option for every patient. Guidelines for patients and physicians still need to be established as the technique begins to be offered in a clinic setting, said Smith. "This is a very new technology and it requires education both of patients and physicians," he concluded. Visit www.cancer.med.umich.edu/clinic/fertilityclinic.htm for information about fertility and cancer.
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