In an analysis reported in the Journal of Clinical Oncology, Park et al found that most of the improvement in breast cancer–specific mortality observed over time in the United States is not explained by tumor size or estrogen receptor status in women aged < 70 years, suggesting a major contribution of treatment to survival improvement. Tumor size and estrogen receptor status contributed more to improvements among older patients.
In the study, hazard ratios were calculated for breast cancer–specific death from time of invasive breast cancer diagnosis in the Surveillance, Epidemiology, and End Results (SEER) 9 Registries database from 1973 to 2010 with and without stratification by tumor size and estrogen receptor status. The registries included 543,171 women with first primary invasive breast cancer and 468,761,934 woman-years of follow-up from 1973 to 2010.
Stratification by Tumor Size
Overall, risk of breast cancer–specific death declined between 1973 and 1979 vs 2005 to 2010 for both the first 5 years after diagnosis and thereafter. Among women aged < 70 years, tumor size explained < 17% of improvements, whereas tumor size explained 49%, 39%, and 20% of improvements in local, regional, and distant disease in women aged ≥ 70 years. Tumor size accounted for more of the improvement in the first 5 years vs thereafter; in women aged ≥ 70 years, tumor size accounted for 86%, 65%, and 36% of improvement for local, regional, and distant disease, whereas tumor size explained ≤ 33% of improvements in those aged < 70 years.
Tumor Size and Estrogen Receptor Status
With additional adjustment for estrogen receptor status in data from 1990 to 2010, tumor size alone explained < 10% of improvement and tumor size plus estrogen receptor status explained > 20% of improvement in breast cancer–specific mortality in women aged < 70 years; in women aged ≥ 70 years, tumor size explained up to 46% of improvement and tumor size plus estrogen receptor status explained up to 61% of improvement. The proportion of improvement in 5-year breast cancer–specific mortality explained by these factors was up to 36% in the younger women and up to 89% in the older women.
The investigators concluded: “Most stage-specific survival improvement in women younger than age 70 years old is unexplained by tumor size and [estrogen receptor] status, suggesting a key role for treatment. In the first 5 years after diagnosis, tumor size contributed importantly for women ≥ 70 years old with local and regional stage, and stratification by tumor size and [estrogen receptor] status explained even more of the survival improvement among women age ≥ 70 years.”
Mitchell H. Gail, MD, PhD, of the National Cancer Institute, is the corresponding author of the Journal of Clinical Oncology article. Ju-Hyun Park, PhD, of Dongguk University, Seoul, and William F. Anderson, MD, MPH, of the National Cancer Institute, contributed equally to the article.
The study was supported by the National Cancer Institute and National Research Foundation of Korea.
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