The demographic and clinical characteristics of African-American (n=162; 16.6%) and white women (n=813; 83.3%) with breast cancer are presented in . Overall, the median follow-up time was 11 years (IQR 4.5–22.4 years). Median follow-up was significantly shorter for African-American women than their white counterparts (median=9 years (IQR 3.0–19.0) vs 12 years (IQR 4.8–22.7), p=0.0003). Among those who survived, African-American women (n=28) and white women (n=193) had similar follow-up (median=24.3 years vs 24.4 years, p=0.07), which suggests that the difference in median survival between African-American and white women is due to increased mortality among African-American women. During this period, there were 753 deaths; 317 were due to breast cancer and 436 were due to other causes. Slightly more African-American women died of breast cancer than white women (37.7% vs 31.5%, p=0.13). There were no racial differences in the proportion of other-cause deaths (44.4% vs 44.8%, p=0.94). The distribution of age was also similar in both groups. Compared with white women, African-American women had significantly fewer years of education (24.7% vs 28.3%, respectively, had ≥12 years of education; p<0.0001), greater mean BMI (28.2 kg/m2 vs 25.9 kg/m2, p<0.0001), and fewer reported adequate financial resources (66.7% vs 86%, respectively; p<0.0001). African-American women were less likely than their white counterparts to have localised disease (43.8% vs 55.6%, respectively; p=0.01) at the time of breast cancer diagnosis. Additionally, African-American women were more likely to have regional disease (48.1% vs 39.2%, respectively; p=0.04), receive no surgery (3.7% vs 1.4%, respectively; p=0.04), and have larger tumours, with mean tumour sizes of 38.2 (SD=26.2) and 32.8 (SD=24.7) millimetres for African-American and white women, respectively (p=0.01).
Characteristics of the study group overall and by race
The distributions of summary measures of functional limitations overall and by race are presented in and distributions of specific functional limitations are presented in A,B. At 3 months after breast cancer diagnosis, African-American women were more likely to report any functional limitations (83.3% vs 67.3%, p<0.0001) and a greater number of functional limitations than their white counterparts (mean 2.8 (SD=2.3) and 2.1 (SD=2.3); p=0.0003). African-Americans were more likely than whites to report difficulty in pushing or pulling large objects (66.1% vs 48%, p<0.0001), lifting less than 10 pounds (33.3% vs 19.3%, p<0.0001), lifting more than 10 pounds (62.4% vs 42.9%, p<0.0001), going up or down a flight of stairs (17.3% vs 11.7%, p=0.05), and walking half a mile (29.6% vs 22.1%, p=0.04). In addition to having a greater mean increase in the number of functional limitations during the first year after diagnosis (0.6 (SD=1.4) vs 0.4 (SD=0.9), p=0.03), a larger proportion of African-American women reported difficulty going up or down a flight of stairs at month 12 but not at month 3 (16.7% vs 9%, p=0.003).
(A) Distribution of functional limitations reported at 3 months following breast cancer diagnosis. (B) Distribution of functional decline between 3 and 12 months following breast cancer diagnosis.
Comparing white women with versus without functional limitations, Kaplan-Meier plots show considerably shorter other-cause survival for those with functional limitations (A, p value for log-rank test <0.0001, appendix). Overall, African-American women with or without functional limitations have shorter survival times than their white counterparts. Borderline statistically significant differences were observed in the survival curves of African-American women with functional limitations and their white counterparts (p value for log-rank test=0.06). Difficulties in pushing or pulling large objects (HR=1.34, 95% CI 1.04 to 1.73), writing or handling small objects (HR=1.56, 95% CI 1.00 to 2.44), walking half a mile (HR=1.60, 95% CI 1.19 to 2.14), each unit increase in the number of self-reported functional limitations (HR=1.08, 95% CI 1.03 to 1.14), as well as experiencing any functional limitation (HR=1.47, 95% CI 1.13 to 1.91) were all associated with statistically significant increases in the risk of other-cause mortality (). Functional decline was not associated with other-cause mortality. When evaluating effect modification by stage, we found that the number of functional limitations (HR=1.11, 95% CI 1.03 to 1.19) as well as 0 vs ≥1 functional limitations (HR=1.46, 95% CI 1.05 to 2.03) were significantly associated with other-cause mortality in women with localised disease but not in those with regional or remote disease, whereas functional decline was associated with increased risk of other-cause mortality in women with regional and remote disease (HR=1.61, 95% CI 1.03 to 2.52), but not in those with localised disease ().
(A) Kaplan-Meier estimates of other-cause survival by race and category of functional limitations (0 vs ≥1). (B) Kaplan-Meier estimates of breast cancer survival by race and category of functional limitations (0 vs ≥1).
HRs (and 95% CIs) of functional limitations for mortality*
HRs (and 95% CIs) of functional limitations for mortality stratified by tumour stage and body mass index*
Breast cancer-specific mortality
Kaplan-Meier plots of breast cancer survival indicate that African-American women had poorer survival than white women (B, appendix). Furthermore, African-American women with functional limitations had significantly poorer survival than those without limitations (p value for log-rank test=0.05). In multivariate models, we found no evidence of an association between any of the measures of functional limitations and breast cancer-specific mortality in this group (). On the other hand, each unit of functional decline (HR=1.17, 95% CI 1.05 to 1.31) and decline in the ability to sit ≥1 h (HR=2.06, 95% CI 1.13 to 3.76) were both significantly associated with increased risk of breast cancer mortality. Each unit increase in the number of functional limitations was positively associated with other-cause mortality in overweight (BMI 25–30; HR=1.17, 95% CI 1.05 to 1.31) and obese women (BMI>30; HR=1.48, 95% CI 1.09 to 2.02), but not in women of normal weight (BMI<25; HR=1.13, 95% CI 0.94 to 1.36; ). Functional decline was positively associated with breast cancer mortality in obese women (HR=3.05, 95% CI 1.32 to 7.03).