In fact, many cancer treatments can impair fertility. And as a precaution, couples are warned to wait at least six months to one year after their last radiation or chemotherapy dose before trying to conceive, Dr. Mulvihill says, although new sperm is cycled in only 90 days. As for eggs, because they are "quiet and not metabolizing," if they survive the radiation blast or chemo dose, "there's no sort of chemistry going on that would make chemo or radiation do a mutation in the ovary," says Dr. Mulvihill.

Future research

Although no effects have been seen so far, the teams of researchers are still teasing apart the data.

For instance, some of the researchers on the project have now built dummies with every inch covered by radiation sensors, so they can measure exactly how much radiation the gonads received from different techniques, different machines, and in different time periods -- radiation doses and the protection offered have changed a lot since the '50s or '60s, Dr. Mulvihill says, when patients getting radiation may not have had their gonads covered by "clamshell" lead casings, currently in wide use.

The researchers are also looking to see if there is any correlation between cancer treatment and the likelihood to have offspring with birth defects among sub-populations -- patients who had, say, especially high-dose therapies, or who were given limited protection.

Ultimately, Dr. Mulvihill wants to see if these treatments cause genetic changes that might be too faint to show up clinically. "Given how unbelievable our hypothesis is," says Dr. Mulvihill, "my swan song is to look at it at the DNA level, when genome sequencing gets cheap enough." He wants to compare a child's DNA against that inherited from his or her parents, to see if an unusually high number of new mutations have cropped up, even among the so-called junk DNA that might not play any role in the child's development.

And those findings could have implications not just for cancer treatment, but for the whole science of genetics. "If our study's sequencing showed changes to junk DNA, and the kids are normal, then maybe it really is junk DNA, because it can be changed without injury to the next generation," Dr. Mulvihill says.

For now, though, Dr. Mulvihill believes the study is a reassuring one for patients and doctors: "Toxicity to gonads [from these treatments] doesn't appear to exist," he says.


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