A new analysis shows a small but surprising upswing during the 1990s in the proportion of women with newly diagnosed breast cancer who have unusually large tumors, which are more likely to prove fatal. Experts are uncertain why this happened, but they speculate that both obesity and hormone replacement therapy may have fueled the growth of larger cancers, even during a time when the discovery of small tumors rose dramatically as a result of widespread mammography.
The analysis, prepared by the American Cancer Society, found that the incidence of large tumors--those five centimeters or larger in size--increased by just over 2% a year between 1992 and 2000 but only in white women. In 2000 there were 6.3 cases of breast cancer larger than five centimeters for every 100,000 white women in the United States, compared with 5.6 cases in 1992. Large tumors are about twice as common in black women. The cancer society attributes this to less access to high-quality screening, particularly for poor women. In 2000 there were 12 cases of large tumors for every 100,000 black women, a figure that changed little throughout the 1990s.
Overall, breast cancer survival is improving. Since about 1990 the breast cancer death rate has been falling by 2.5% annually for whites and 1% for blacks. Experts say they think better treatment, including widespread use of the drug tamoxifen, as well as mammogram screening are responsible for the improvement.