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Breast Cancer Survival Gains Due to Smaller Tumors
Aug. 8, 2005 A big part of the progress made in
treating breast cancer has occurred because the tumors found in women
are getting smaller. The shift to smaller early-age tumors accounted for
almost all of the improvement in survival for senior citizens over 64
years of age.
A new study finds that the size of newly diagnosed
breast cancers has shifted towards smaller tumors, even within
conventional cancer stage categories, and that this shift accounts for a
proportion of the improvement seen in breast cancer survival over the
last 30 years.
The authors of the report say that failure to
account for this shift in tumor size can lead to overestimation of the
impact of treatment advances. The study is published in the September
15, 2005 issue of CANCER, a peer-reviewed journal of the American Cancer
Society.
Great strides in breast cancer survival have been
made over the last 30 years, overall and within cancer stages,
coinciding with advances in treatment and with increased use of
screening mammography. However, if important prognostic factors have
also changed over time, then observed improvements in breast cancer
survival may be a result of such changes and of improvements in
treatment.
The authors studied changes in tumor size because
it is a strong predictor of breast cancer prognosis and it is a
straightforward, reliably evaluated, consistently available measure.
Elena B. Elkin, Ph.D. of the Memorial
Sloan-Kettering Cancer Center in New York and her colleagues reviewed
data on early-stage breast cancers from the Surveillance, Epidemiology
and End Results (SEER) program to look for trends in tumor size and
explore how those trends might impact survival rates. SEER is a
population-based cancer registry system that collects and monitors data
on cancers diagnosed in certain areas of the U.S.
Among localized and regional breast cancers, the
size of newly diagnosed tumors decreased significantly from 1975 through
1999.
While breast cancer survival rates improved during
this time, adjusting for the changes in tumor size diminished the
magnitude of the survival increases within each stage category.
When the researchers compared five-year cancer
survival rates in women diagnosed 1995-1999 with survival rates in women
diagnosed 1975-1979, they found that the shift toward smaller tumors
explained 61 percent of the survival increase in localized breast cancer
and 28 percent of the survival increase in regional breast cancer.
"Failure to adequately control for this
[within-stage tumor size] shift leads to inflated estimates of the
impact of secular changes in treatment on stage-specific survival,"
conclude the study's authors. They add, "size-standardization is a
refinement...that greatly improves our ability to interpret
trends in
breast cancer survival."
Source:
Article: "The Effect of Changes in Tumor Size on
Breast Carcinoma Survival in the U.S.: 1975-1999," Elena B. Elkin,
Clifford Hudis, Colin B. Begg, Deborah Schrag, CANCER; Published Online:
August 8, 2005 (DOI: 10.1002/cncr.21285); Print Issue Date: September
15, 2005.
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