MONDAY, Aug. 8, 2005 (HealthDay News) -- Improved breast cancer survival rates over the past 30 years are linked to smaller tumors at the time of diagnosis, new study findings suggest.
The report, which will be published in the Sept. 15 issue of Cancer, also said that failure to account for this trend toward smaller breast cancer tumors at the time of diagnosis can lead to an overestimation of the impact of advances in breast cancer treatment.
Researchers analyzed data from the U.S. Surveillance, Epidemiology and End Results (SEER) program -- a population-based cancer registry system -- to identify trends in breast cancer tumor size, and how those trends might affect survival rates.
The investigators found that the size of newly diagnosed breast cancer tumors decreased significantly from 1975 to 1999. The researchers then compared five-year breast cancer survival rates in women diagnosed from 1995-1999 with those diagnosed from 1975-1979. They found that the trend toward smaller tumors explained 61 percent of the survival increases in localized breast cancer and 28 percent of the survival increase in regional breast cancer.
"Failure to adequately control for this shift leads to inflated estimates of the impact of secular changes in treatment on stage-specific survival," the study authors concluded.
The American Cancer Society has more about breast cancer.