BOSTON -- Despite many strides in fighting breast cancer, not all the numbers are positive, according to a new study.

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NewsCenter 5's Liz Brunner reported that when it comes to breast cancer, the survival rate is encouraging. Since 1990, breast cancer deaths have been falling at an annual rate of 2.5 percent for white women and 1 percent for black women.

"Larger tumors are more extensive; they metastasize, and they are therefore harder to treat and to cure," said Dr. David Rosenthal of the American Cancer Society.

And they're increasing among some newly diagnosed women, according to a study released Tuesday. The study found the number of large breast tumors -- those 5 centimeters or more -- rose just over 2 percent between 1992 and 2000, but only in white women.

"I don't know the answer," said Rosenthal. "But most people are suspecting that it could be because of hormone replacement therapy or because of obesity or increased weight."

Dr. Daniel Kopans doubted these suggestions. He attributed the rise to an increase in the number of women getting mammograms, most of which show no signs of breast cancer.

"My concern is that as we've done more and more screening and finding the small cancers and decreasing the death rate, some women have become falsely reassured by the fact that their mammogram was negative," said Kopans.

A false negative could result in ignoring lumps until the disease has progressed. That's why most experts and cancer survivors stand by the need for early detection.

Social worker Sandy McLaughlin was diagnosed with a breast tumor when she was 35 and said she's grateful she found her tumor when it was still small.

"You know, I think people are afraid sometimes to have mammograms done 'cause they're afraid of finding it, but actually if you find it, it's much more manageable," said McLaughlin.

While the number of large tumors increased among white women, it remained the same among African-Americans. Still, large breast tumors are about twice as common among blacks as whites. The American Cancer Society attributes disparity to the fact that black women are more apt to have less access to high-quality screening.