UC San Diego

115 Background: Larger social networks have been associated with better breast cancer survival. To investigate potential mediators, we evaluated associations of social network size and diversity with lifestyle and treatment factors associated with prognosis. Methods: We included 9,331 women from the After Breast Cancer Pooling Project who provided data on social networks within two years following diagnosis. A social network index was derived from information about the presence of a spouse or intimate partner, religious ties, community participation, friendship ties, and numbers of relatives. Diversity was assessed as variety of ties, independent of size. We used logistic regression to evaluate associations with outcomes and evaluated whether effect estimates differed using meta-analytic techniques. Results: Associations of social networks and outcomes generally did not differ by cohort. Because of the low prevalence of smoking and alcohol consumption in the Shanghai cohort, however, analyses of smoking and alcohol included US cohorts only. Women who were socially isolated (small networks) were more likely to be obese (body mass index>30 kg/m2, OR=1.21, 95% CI:1.03-1.42) and have low physical activity (<10 MET-h/wk, OR=1.53, 95% CI:1.34-1.75) compared to socially integrated women. Women with low network diversity were more likely to be current smokers (OR=3.68, 95% CI:2.19-6.19) and have high alcohol consumption (>15 g/d alcohol, OR=2.43, 95% CI:1.60-3.69). Among node positive cases, socially isolated women were more likely not to receive chemotherapy (OR=1.52, 95% CI:1.03-2.25). By contrast, low network diversity, but not social network size, was associated with greater odds of not receiving adjuvant hormonal therapy (OR=1.52, 95% CI:1.03-2.23). Associations with surgery were nonsignificant. Conclusions: In a large pooled cohort, small, less diverse social networks measured post-diagnosis were associated with more adverse lifestyle factors and less intensive cancer treatment, which may help to explain poorer breast cancer prognosis in socially isolated women.