Understanding the Effects of Cancer-Related Factors on the Association Between Physical Activity, Self-Efficacy and...

Breast cancer can negatively impact survivors' physical activity (PA). Social cognitive theory (SCT) constructs may be correlated with PA, but it is unclear if cancer-related factors affect these relationships.

To examine associations between PA, self-efficacy, social support, and exercise barriers interference in breast cancer survivors and whether cancer-related factors moderate these relationships.

Baseline data from 341 post-primary treatment breast cancer survivors in a web-based diet/exercise intervention trial were analyzed. SCT constructs, accelerometry-measured and self-reported moderate-to-vigorous physical activity (MVPA), and cancer-related factors (stage, time since diagnosis, history of chemotherapy, history of radiation, and hormone therapy status) were examined using Pearson correlation analysis and multivariable linear regression analyses.

Exercise barriers interference was inversely associated with self-reported (r = -0.272, p < 0.001); and accelerometry-measured MVPA (r = -0.128, p = 0.020). No other statistically significant associations were found. Stage and history of chemotherapy moderated the association between social support and self-reported MVPA. The association was stronger among survivors diagnosed with DCIS/stage I versus stage II/III (β = 4.14, p = 0.043, CI = -2.20-10.49) and weaker among individuals who previously received chemotherapy versus no chemotherapy history (β = -5.02, p = 0.026, CI = -11.51-1.47); effects were independent of one another.

Cancer stage and previous chemotherapy moderate the association between social support and MVPA. Targeting social support in early-stage breast cancer survivors or survivors that did not receive chemotherapy may improve intervention effectiveness.