Introduction The incidence of breast cancer is increasing in Brazil. Breast cancer is a major cause of morbidity and mortality with major social and epidemiological impact. The aim of this study is to evaluate the association between social support before treatment for breast cancer and quality of life (QOL) 6 months after starting treatment.

Methods Eligible participants were women who were treated for incident breast cancer in the National Cancer Institute between June 2009 and March 2010. EORTC QLQ-C30 was used to measure QOL. MOS-SSS was used to assess social support prior to treatment. Bivariate analyses of dichotomous variables were carried out and ORs with 95% CI were presented.

Results 195 women were evaluated. Good emotional support was a protective factor for overall health (OR 0.42 (95% CI 0.23 to 0.79)) and scale functionality (OR 0.36 (0.18 to 0.71)). Information support was associated with better global health (OR 0.41 (0.22 to 0.76)), functionality (OR 0.35 (0.18 to 0.70)) and symptoms scale (OR 0.38 (0.18 to 0.77)). Women who reported good emotional support were 70% less likely to report general health problems 6 months after starting treatment (0.13–0.65).

Conclusion The results of this study suggest that a good social environment prior to treatment is positively associated with QOL 6 months after starting treatment in women with breast cancer, underscoring the importance of assessing social environment.