A team led by medical oncologist Dr Rowan Chlebowski analyzed data obtained from the prospective randomized phase III Women's Intervention Nutrition Study, which began in 1994 and involved 2,437 women from 37 states aged between 48 and 79 years. All were receiving standard care following the removal of their tumors.
After around five years, 9.8 percent of the 975 women who consumed a low-fat diet with an average daily intake of 33.3 g of fat suffered a recurrence of their cancer. On the other hand, 12.4 percent of the 1462 patients on a standard diet with daily fat consumption averaging 51.3 g experienced a relapse.
"This study may well represent the first lifestyle change, namely lowering dietary fat intake, that can have a favorable effect on breast cancer outcome," said Chlebowski.
Although the study was originally designed to measure the effect of a low fat diet on recurrence of all types of cancer, the most significant results were seen in women with estrogen-negative cancers, which are generally considered to be a marker for poorer prognosis.
The risk of recurrence was reduced by 42 percent for these women, compared with just 15 percent for women with estrogen receptor-positive cancers.
Chlebowski's findings were presented at the annual meeting of the American Society for Clinical Oncology (ASCO) on Monday but have yet to be published in a journal.
ASCO president elect Dr Sandra Horning said the study was one of several presented at the meeting suggesting that cancer survivors can take relatively simple measures to reduce the chance of the disease. Another indicated that colon cancer patients who use asprin in conjunction with standard therapies reduced the risk of recurrence and lengthened their survival chances.
Although he says that the results of his study may mean women have an "additional option within their control for reducing the risk of breast cancer recurrence", Chlebowski is not deceived that his results are the final word on the matter.
He said that further studies of women with ER-positive and ER-negative breast cancers are needed to test the hypothesis.
"If these results are confirmed in additional trials, reduction of dietary fat intake could be considered part of the management of breast cancer in postmenopausal women."
American Cancer Society's deputy chief medical officer, Len Lichtenfeld, joined him in calling for further investigation:
"We've been hearing about the potential of low-fat diets to affect cancer for decades," he said. "Until now, we had no evidence this had a significant impact. Now we have some, but it really has to be confirmed in larger trials."
Neither Chlebowski nor Lichtenfeld advocates diet as a stand-alone cancer treatment.