Breast Cancer in Native American Women: A Population Based Outcomes Study involving 863,958 Patients from the Surveillance Epidemiology and End Result (SEER) Database (1973-2010)
Author(s): Shilpa Gopinath, Gopinath KV
Background: Breast cancer is the most common cancer among Native American (NA) women. Despite this fact, existing data suggests NA women have a lower-than-expected breast cancer incidence rates, but a markedly higher mortality to incidence ratio compared to other racial/ethnic groups. This study sought to analyze demographic and clinical factors in a large NA breast cancer cohort to validate these observations and to delineate clinical and pathological factors which may better risk stratify this unique population for optimal treatment protocols and clinical trial accrual.
Methods: Demographic and clinical data on 863,958 women with carcinoma of the breast was extracted from the Surveillance Epidemiology and End Result (SEER) database (1973-2010). Standard statistical methodology was used.
Results: Among 863,958 breast cancer patients, 4,289 (0.5%) were NAs and 859,669 (99.5%) were non-Hispanic white (NHW) women. The majority of breast cancer in both groups occurred among those aged 60 to 79 years (33.5% NA vs. 43.7% NHW). NA women had a higher incidence of breast cancer at a younger age (9.2% NA vs. 5.1% NHW for age 20-39, and 51.8% NA vs. 38.1% NHW at age 40-59; p<0.001), and a higher rate of regional (34.0%NA vs. 31.2%NHW) and distant metastasis (7.9%NA vs. 6.1%NHW). The majority of women in both groups had tumor size <2 cm (56.4%) and moderately differentiated tumor (42.3%; p<0.001). Mean overall survival (OS) was significantly longer in NHW women than NAs (7.40±6.7 vs. 6.66±6.1 years; p<0.001). The majority (54.3%) of all patients underwent surgery only. Cancer specific mortality (21.7%NA vs. 21.2%NHW) and 1-year cumulative survival (94%) was similar between the two groups. The 5-year survival rate was lower in NA women (74%NA vs. 76% NHW). Multivariate analysis identified that age>60 (OR 1.3), size >4cm (OR 1.8) and distant metastasis (OR 3) were associated with increased mortality; p<0.001.
Conclusions: Breast cancer affects the NA population far less often than NHW women. NA breast cancer patients tend to be younger and present with more aggressive disease features and have lower survival rates compared to women in other ethnic groups. Surgical resection and combination surgery and radiation treatment confers the greatest survival advantage in NA women compared to NHW. In light of these disparities, and to better understand the breast cancer burden and associated risk factors, NA women should be considered for clinical trial accrual to delineate genetic and environmental factors which influence incidence rates and prognosis.