In 1976, he became chief of the institute's clinical epidemiology branch, a position he held until 1994.

In planning the latest studies, said Dr. Arthur Schatzkin, chief of the nutritional epidemiology branch at the cancer institute, "we had high expectations and good rationale."

Dr. Shelia Zahm, deputy chief of the occupational epidemiology branch at the National Cancer Institute, said the new study was "certainly a strong piece of evidence against the hypothesis."

Conducting research on silicone implants in a climate that is infused with legal charges and countercharges has not been easy, said Dr. Louise Brinton, chief of the environmental epidemiology branch of the National Cancer Institute.

But Dr. Arthur Schatzkin, who is the chief of the nutritional epidemiology branch in the National Cancer Institute's division of cancer epidemiology and genetics, said that people want answers, even if they are not definitive.

Dr. Shelia Zahm, deputy chief of the occupational epidemiology branch at the National Cancer Institute, said "there's not a lot of information linking environmental exposures to breast cancer," even though researchers have looked.

"Everybody knows overweight and obesity are risk factors for heart disease and diabetes," says Arthur Schatzkin, MD, DrPH, chief of the nutritional epidemiology branch and senior investigator at the National Cancer Institute.

Schatzkin, chief of the nutritional epidemiology branch of the National Cancer Institute in Bethesda, Md., helped lead one of the studies, called the Polyp Prevention Trial.

"It's provocative," said Dr. Regina G. Ziegler, an epidemiologist at the nutritional epidemiology branch of the National Cancer Institute.

"This is an experienced group," said Dr. Arthur Schatzkin, senior investigator in the nutritional epidemiology branch of the National Cancer Institute.