Pain in long-term breast cancer survivors: the role of body mass index, physical activity, and sedentary behavior
Although pain is common among post-treatment breast cancer survivors, studies that are longitudinal, identify a case definition of clinically meaningful pain, or examine factors contributing to pain in survivors are limited. This study describes longitudinal patterns of pain in long-term breast cancer survivors, evaluating associations of body mass index (BMI), physical activity, sedentary behavior with mean pain severity and above-average pain. Women newly diagnosed with stages 0–IIIA breast cancer (N = 1183) were assessed, on average, 6 months (demographic/clinical characteristics), 30 months (demographics), 40 months (demographics, pain), 5 years (BMI, physical activity, and sedentary behavior), and 10 years (demographics, pain, BMI, physical activity, and sedentary behavior) post-diagnosis. This analysis includes survivors who completed pain assessments 40 months post-diagnosis (N = 801), 10 years post-diagnosis (N = 563), or both (N = 522). Above-average pain was defined by SF-36 bodily pain scores ≥1/2 standard deviation worse than age-specific population norms. We used multiple regression models to test unique associations of BMI, physical activity, and sedentary behavior with pain adjusting for demographic and clinical factors. The proportion of survivors reporting above-average pain was higher at 10 years than at 40 months (32.3 vs. 27.8 %, p < 0.05). Approximately one-quarter of survivors reported improved pain, while 9.0 % maintained above-average pain and 33.1 % reported worsened pain. Cross-sectionally at 10 years, overweight and obese survivors reported higher pain than normal-weight survivors and women meeting physical activity guidelines were less likely to report above-average pain than survivors not meeting these guidelines (p < 0.05). Longitudinally, weight gain (>5 %) was positively associated, while meeting physical activity guidelines was inversely associated, with above-average pain (OR, 95 % CI = 1.76, 1.03–3.01 and 0.40, 0.20–0.84, respectively) (p < 0.05). Weight gain and lack of physical activity place breast cancer survivors at risk for pain long after treatment ends. Weight control and exercise interventions should be tested for effects on long-term pain in these women.