57% decline in Rhode Island invasive breast cancer mortality between 1987 and 2017: mammography predominates in preventing mortality

Background Controversy exists regarding proportional contributions of mammographic screening versus systemic therapy to declining disease-specific mortality of female invasive breast cancer (IBC) in the United States. Understanding relative contributions may help address allocation of medical resources. Methods A 31-year (1987-2017) review of Rhode Island (RI) Cancer Registry data of female IBC was carried out in a state with high rates of mammographic screening. Results Over 31 years in RI, statistically significant improvements occurred at initial diagnosis of IBC: mean and median maximum cancer diameters decreased by 21% and 30% respectively. Despite 1997 introduction of more accurate sentinel lymph node biopsy, the proportion of patients with axillary lymph node metastases (LNM) decreased by 27%. Extent of LNM also decreased as patients with over three node metastases decreased 67%. By 2017, 53% of all patients with LNM had only one. Poorly differentiated cancers decreased 50%. Disease-specific mortality decreased 57%. Discussion Improvements in initial presentation of IBC are consistent with most having progressive growth, from cellular origin to palpable mass, the currently accepted biological model. Breast cancers identified earlier at initial diagnosis through screening mammography are characterized by smaller size, fewer axillary LNMs, better grade differentiation, and decreased mortality. Statistical analysis from these improved diagnostic parameters indicate that the majority of mortality decline from invasive breast cancer in RI can be attributed to earlier detection. Thus, mammography predominates in preventing mortality.