Predicting the return of breast cancer.

High-fat diets have long been implicated in the development of breast cancer. Now, epidemiologists have evidence suggesting that obese women who have already suffered one bout with breast cancer are more likely to suffer a recurrence.

Ruby T. Senie of the Centers for Disease Control in Atlanta and her colleagues conducted a 10-year study of 923 breast cancer patients age 24 to 95. Using the Metropolitan Life Insurance height-weight charts, the researchers classified 22 percent of the women as obese -- that is, 25 percent over their ideal weight. All 923 women had undergone surgery to remove the primary tumor soon after the cancer was diagnosed.

The researchers used a statistical method to account for several factors that can influence the risk of recurrence, including size of the original tumor, the patient's age at diagnosis and whether or not she received anticancer drugs after surgery. When the team accounted for those factors, they discovered that obesity increased the risk of recurrence by 30 percent. Among women who showed no sign of cancer in their lymph nodes, obese individuals ran a 60 percent greater risk of cancer recurrence than thinner women.

This supports previous data hinting at obesity's link to breast cancer recurrence, notes Rowan Chalebowski, a cancer researcher at the Harbor-UCLA Medical Center in Torrance. Obese women may eat a high-fat diet that predisposes them to another bout with cancer, he says.

On the other hand, obese women tend to produce more estrogen, a female sex hormone that fuels the growth of some breast tumors, Senie says. After surgical removal of the primary tumor, high concentrations of estrogen in the blood-stream may encourage the proliferation of tiny seeds of cancer that escaped the surgeon's knife, she notes.

Can obese women reduce the threat of breast cancer's spread by losing weight after diagnosis? Maybe. But some researchers believe that the high-estrogen environment that may have existed in obese women prior to diagnosis somehow primes a developing tumor. If that's true, then a weight-loss program after the fact won't do much good.

Senie speculates that not all tumors fall into that category and that a weight-loss program after diagnosis might indeed help some women prevent a cancer recurrence.

The best advice of all: Lose weight while you're still healty. Scientists don't know whether obesity increases the risk of developing breast cancer, but they do know that too much body fat boosts the threat of other illnesses, including heart disease. The suggested link to breast cancer recurrence simply adds to the list of reasons to shed excess weight, Senie says.