Another equally troubling but rarely considered question is: Could the cancer affect the unborn child?

In a rare case, cancer from a young mother with lymphoma may have been passed to the fetus, said Howard Weinstein, MD, the mother's primary physician at Massachusetts General Hospital in Boston. A report on the case was published in a recent issue of The New England Journal of Medicine (Vol. 341, No. 2).

The 15-year-old mother showed no symptoms of illness until two weeks before her due date. She was diagnosed with an aggressive case of lymphoma, a cancer of the lymph nodes, and died 18 days after delivering a boy by Cesarean section. Her baby soon showed signs of lymphoma and died two months later.

"We were absolutely astounded," said Dr. Weinstein. "This happens very, very rarely, and no one really knows why it happens. The placenta is a pretty good barrier, especially for tumor cells. It was a mystery why this happened to our patient."

In an accompanying editorial, Robert Resnick, MD, of the University of California, San Diego, stated a recent review showed 19 cases of malignant melanoma that had spread to the mother's placenta. "In five of these cases the tumor extended into the fetus, which died of metastatic melanoma in four of the five cases," Dr. Resnick wrote. Similarities in leukemia cells in the mother and fetus were documented in the March 1, 1990, issue of the journal Cancer by Sachiko Osada, MD, of the department of pediatrics, and his colleagues at the Nagoya School of Medicine in Nagoya, Japan.

Cancer During Pregnancy: What are the Odds?

Although the chances of a mother and fetus sharing cancer cells are extremely rare, cancer occurring during pregnancy is not particularly rare. Cancer occurs in one of every 1,000 pregnancies, and half are tumors of the uterine cervix, breast, or thyroid, which can spread to the placenta but will not harm the fetus. Leukemia/lymphoma and melanoma cells are more aggressive and seem more likely to get past the placenta, said Dr. Weinstein. "There really is no documented proof about this," he added. "Our laboratory reports represent the best evidence so far."

Cancer during pregnancy is typically a very treatable condition, said Ralph Vogler, MD, scientific program director for the American Cancer Society (ACS). "The majority of tumors are slow-growing tumors, and doctors may wish to wait past the first trimester -- the most critical period -- before starting chemotherapy." However, radiation doses can be fine-tuned so they are safe for the fetus, even during the first trimester, he said.

"A cancer diagnosis is certainly not a death knell for mother or baby," added Dr. Vogler. "Very much can be done safely."