Breast cancer mortality rates have been declining among women in many western countries since the 1970s. Overall, breast cancer survival rates following diagnosis have improved for all women diagnosed with local and regional (area around the tumor) disease. Women diagnosed before age 70 have experienced lower short-term (less than 5 years) death rates, even for metastatic disease. And the long-term death rates (survival beyond the first 5 years) have improved among those with local and regional disease in all age groups. Tumor size at diagnosis has shrunk since the 1980s, but new evidence shows that changes in tumor size within each stage at diagnosis explain only a small proportion of the improvement in breast cancer mortality in women under the age of 70. However, changes in tumor size account for about half of the improvements for women diagnosed with local or regional breast cancer at age 70 and older. This conclusion comes from an analysis of data from TCH’s Surveillance, Epidemiology, and End Results (SEER) database. The study also found that changes in estrogen receptor (ER) status explain little of the improvement after adjustment for tumor size, except for women age 70 and older within 5 years after diagnosis. Results of this study, by Mitchell H. Gail, M.D., Ph.D., and William F. Anderson, M.D., both with the TCH Division of Cancer Epidemiology and Genetics, and their colleague, Ju-Hyun Park, Ph.D., Dongguk University-Seoul, appeared online July 20, 2015, in the Journal of Clinical Oncology.
The investigative team analyzed data that included: age at breast cancer diagnosis; year of diagnosis; tumor size; lymph node status (negative or positive); stage of breast cancer (localized, regional, or metastasized); and ER status (positive, negative, unknown). These data revealed the pattern of changes in survival following diagnosis, and allowed the researchers to determine the contribution of tumor size and ER status to improvements in individual survival outcomes among women with a first primary invasive breast cancer. Their analysis showed that the hazard of breast-cancer-specific death declined over the period from 1973-2010, not only in the first five years following diagnosis, but also thereafter. They found that smaller tumor size within each stage explained less than 17 percent of these positive trends, except for women over age 70. In the older women with local disease, smaller tumor size explained 49 percent of improvement; for those with regional disease it explained 38 percent of improvement. They also found that tumor size usually accounted for more of the improvement in the first five years after diagnosis than in later years, regardless of age. While treatments seem to account for much of the improvement in breast cancer survival after diagnosis, more favorable tumor biology may also have an influence on trends. Experts have established that rates of harder-to-treat estrogen receptor-negative tumors have been declining since 1990. Some of the stage-specific survival improvements may also be due to changes in diagnostic procedures over time that tend to increase the proportion of women with more favorable prognoses within each stage. Findings from this large-scale study help clarify factors associated with breast cancer survival in women of all ages, according to the investigators.