Background: Long-term effects of breast cancer and its treatment can negatively impact survivors’ physical activity behaviors. Social cognitive theory (SCT) constructs (self-efficacy, social support, exercise barriers) can be determinants of physical activity, but it is unclear if cancer-related factors affect these relationships. We examined associations between physical activity and self-efficacy, social support, and exercise barriers interference in breast cancer survivors and whether cancer-related factors moderated these relationships.
Methods: This is a cross-sectional study of baseline data from 341 post-primary treatment breast cancer survivors enrolled in a randomized controlled trial testing a web-based diet and exercise intervention. Measures included SCT-constructs (barriers self-efficacy, social support, and exercise barriers interference) and moderate-to-vigorous physical activity (MVPA) measured by accelerometry and self-report. Pearson’s correlation coefficients examined associations between SCT-constructs and MVPA. Regression analyses assessed whether cancer-related factors (stage [DCIS/stage I vs. stage II/III], time since diagnosis [≤24 months vs. >24 months], history of chemotherapy [yes vs. no], history of radiation [yes vs. no], and current hormone therapy status) moderated the associations between SCT constructs and MVPA.
Results: A modest inverse association existed between exercise barrier interference and self-reported MVPA (r= -0.272, p<0.001); and accelerometry-measured MVPA (r= -0.128, p=0.020). No other SCT variables were statistically significantly associated with MVPA levels. Stage and history of chemotherapy were found to moderate the association between social support and self-reported MVPA such that the association was stronger among survivors diagnosed with DCIS/stage I vs. stage II/III (b= 4.14, p=0.043, CI= -2.20-10.49) and weaker among individuals with history of chemotherapy vs. no history of chemotherapy (b= -5.02, p=0.026, CI= -11.51-1.47); these associations were independent of one another. No other moderating effects were found.
Conclusion: Cancer stage and previous chemotherapy moderated the association between social support and MVPA. Targeting social support in early-stage breast cancer survivors or who did not receive chemotherapy may improve intervention effectiveness.