According to a new study, a lot of the advancement in breast cancer survival in recently is due to average tumor being smaller, not due to treatments being better.

Researchers have concluded that smaller tumor sizes account for 61% of the improvement in surviving when cancer had not spread beyond the breast, and 28% when it had spread slightly. These results came from examining twenty five years of cancer records nationwide.

For women sixty five and older with early stage tumor the most common scenario, the shift in size accounted for almost all of the improvement in surviving.

“We don’t want to diminish the benefits we’ve seen from advances in treatment because they’ve been fantastic,” said lead researcher Jenny Johnson. “But not all of the advances in survival is due to treatment when important things like size have also changed over time.”

The study was not created to figure out the value of mamograms or treatments. However it implies much about the value of early detection.

“This really helps to show the importance of screening,” said Jessie Dasplow, who supervises breast cancer research at a Cancer Society. “In addition to finding more smaller tumors, we are also finding less big tumors.”

The study was conducted by doctors at Memorial Sloan Ketering Cancer Center in NY and used a federal government database that includes 9 cancer registries covering 10% of the US population. Over 260,000 breast tumors were looked at and analyzed.

Breast cancer is the most common type of cancer in American females. An estimated 211,000 new cases and 40,000 deaths are expected this year due to this type of cancer.

This is the largest research in American females to look at size within early stages. “Even within the same stage category, the average tumor size is smaller today than it was twenty five years ago,” Johnson said.

Survival rates have increased, but scientists have argued over how much of that is because of better medication or tumors being found at early stages. Two-thirds of breast cancers these days are diagnosed at the local stage, while they are still confined to the breast; while in the 70s, only half of them were.

For instance, the number of local-stage breast cancers that were smaller than 1 centimeter rose from less than 10 percent from the year 1975 through 1979 to 25% from the year 1995 through 1999. An inch is about 2.5 Centimiters. Of regional-stage cancers those that spread to nearby tissue or lymph nodes but not widely throughout the body the part that were smaller than 2 centimiters rose from one fifth to one third.

Next, scientists compared 5-year survival rates for these time periods, taking into account the shift in tumor size. For females with local-stage breast cancers, survival rose from nearly 91% to more than 97%, but was only 93% after adjusting for smaller tumors. Look at it another way, the shift in size accounts for 61 percent of the improvement in survival rates.

For regional cancers, survival rose from about 68% to about 80%, but was only 76% once tumor size was factored in. Size made a much bigger difference for older females than younger ones. A whopping 96% of the survival improvement for women Sixty Five and older with local-stage cancers was explained by this. Only 38% of the improvement in females under Fifty was due to the shift in tumor size. “It isn’t necessarily because treatment works better for certain females, it reflects who’s getting more,” because younger females are more likely to receive chemo-therapy, Johnson said. It also shows that older females have benefited from mammograms, Dasplow said.

Federal research shows that the percent of females 40 and older who had a mammogram in the previous two years increased from 29% in 1987 to 70% in 2000. The federal government recommends that females over 40 get mammograms every 1 to 2 years, with or without a breast exam by their doctors. However, Dr. Barnet Kramar, associate director for disease prevention, noted that the study did not have information on how many of these tumors were found through mammograms or what treatments various groups of females received, so no direct assumptions or conclusions about the value of these can be drawn.