While the study found differences in hazard ratio for age-specific survival, improved care and better treatment options might have resulted in increased survival, the authors deduce.
Evaluation of the hazard ratio from time of invasive breast cancer (BC) diagnosis to cancer-specific death from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) 9 Registries database from 1973 to 2010 indicated improved survival based on treatment, especially in women less than 70 years of age.
For this study published in the Journal of Clinical Oncology, which included 543,171 women with primary invasive breast cancer, the authors examined improvements in the hazard ratio (HR) for breast cancer—specific death and breast cancer–specific survival following diagnosis, based on tumor size (from 1973 to 2010) and estrogen receptor (ER) status (1990 to 2010). Notably, women younger than 50 years had larger tumors, had less of a local-stage disease, were usually positive in their lymph nodes, and had a higher rate of ER-negative disease.
When data were compared with 1973 to 1979, HRs decreased steadily over time for women <70 years of age in the first 5 years after diagnosis, even among those with invasive disease. In women ≥70 years of age, improvements were observed among women with local or regional disease, more so among younger women. When the authors compared data from 2005 to 2010 with data from 1973 to 1979, tumor size explained less than 17% of the improvement in HR for death in those <70 years of age, while in the older population the percentages explained were 49%, 39%, and 20% for local, regional, and distant disease, respectively. For 5 years after diagnosis, HR for death decreased for all age groups for women with both local and advanced disease. Tumor size explained less than 10% of the improvement in women <70 years of age and less than 22% in women ≥70 years.
For data from 1990 to 2010, HRs were compared with 1990 to 1994; small improvements in breast cancer—specific death were observed in the first 5 years after diagnosis in women ≥70 years of age with local disease. Tumor size and ER status did not significantly explain improvements in younger women, but in the older population, tumor size explained 46% and combined with ER status, explained as much as 61% of improvement in HR. HR for breast cancer–specific death 5 years after diagnosis declined for women with local disease and could not be significantly explained by the tumor size or ER status.
The authors presume that factors other than tumor size or ER status accounted for most of the stage-specific survival improvements observed in women >70 years old. “Better care associated with fewer patients with unknown ER status may have also improved the prognosis among women age ≥70 years in the first 5 years after diagnosis,” they conclude.