A published case of a rare cancer transmission from mother to fetus drew headlines from around the world when it was published in a leading journal Monday -- but doctors said they worry it will create the misimpression that cancer can be routinely contagious.
The paper, published in the Proceedings of the National Academy of Sciences, documented a case in Japan in which an 11-month-old baby girl was found to have a tumor with an identical genetic signature to a cancer in her mother.
There had been about 30 suspected cases of cancer transmission over the past century, but this is the first case where it has been proved the cancer in the baby came from the mother.
However, given the rarity of the case, doctors say the attention may do more harm than good.
"They are creating alarms in people who will come to believe that cancer is contagious and that this transmission from mother to fetus of cancer represents a process that is common enough for the general public to learn about," said Robert Weinberg, director of the MIT Ludwig Center for Cancer Research and a leading expert in the field of cancer genetics, in an e-mail to ABC News.
He placed the odds of cancer transmission from mother to child at less than one in a million -- though he said an exact number would be impossible to calculate because there have been so few cases. He said the case would be of interest to immunologists to help answer questions about why the mother's immune system does not attack the fetus, and why the baby's developing immune system does not attack foreign bodies in the mother.
While noting the importance of the case to research, even the authors of the research paper said it was so rare that the average person should not worry about it.
"We are pleased to have resolved this longstanding puzzle," said Mel Greaves, a professor of cell biology at the Institute of Cancer Research in the United Kingdom and the study's lead author in a release. "But we stress that such mother to offspring transfer of cancer is exceedingly rare and the chances of any pregnant woman with cancer passing it on to her child are remote."
Because of the rarity of cases of maternal-fetal cancer transmission, a number of cancer experts at major medical centers declined to comment on the article for ABC News.
Dr. Lucas Wong, a hematologist-oncologist at Scott & White Healthcare in Temple, Texas, said the placental barrier typically prevents cancer cells from entering the body of the fetus.
"That's why you can treat a woman with breast cancer and she has a normal baby afterward," he said.
Even in the rare cases of a cancer that could be transmitted, the study does not yet offer a way to know in advance.
"Does that mean you can screen all your children? No, I think it's too preliminary," said Wong.
Weinberg said that for the public, much greater concerns about cancer exist, such as how one would typically get it, how it is diagnosed and how to get it treated.
So while the case may be an interesting one, people should not be concerned they will ever see it in their own lives.
"This does not make it on my list of things for the average layman to worry about, by a mile," said Weinberg.