While we have previously described that adult sarcoma survivors are less active than their siblings [12
], our current analysis allowed us to 1) describe their activity patterns compared to the general population and 2) specifically characterize a phenotype of the sarcoma survivor at greatest risk for a poor activity outcome in this cohort. The prevalence of inactivity in our study (58.9%) is higher than the 50.1% among individuals with impaired mobility status and lower than the 75% among individuals with diabetes reported by investigators who used data from the National Health Interview Survey [29
]. In our analysis, being female, having a hemipelvectomy, and having received platinum or vinca alkaloid chemotherapy were associated with increased risk for physical inactivity. Demographic and personal factors (smoking, obesity depression, cancer pain, anxiety, or low income) were not associated with inactivity in our analysis.
Some treatment factors were predictors of poor activity behaviors. An important finding in this study is that there is an association between two classes of chemotherapeutic agents, vinca alkaloids and platinums, and physical inactivity. Both vinca alkaloids and platinum chemotherapeutic agents are known for their neurotoxic impact on the peripheral nervous system. The resulting chemotherapy-induced peripheral neuropathy (CIPN) has been reported in patients during and after treatment for many childhood cancers, including adolescents and young adults treated for sarcomas [8
]. Peripheral neuropathies typically present during treatment, and although they may diminish over time, such deficits are likely to persist in many survivors [31
]. In adolescents and young adults previously treated for sarcoma, evidence of persistent symptoms of neurotoxicity from cisplatin exposure have been reported, including decreased deep tendon reflexes and increased vibration sensation thresholds [8
]. Persistent neuropathy in lower extremities may account for the balance deficits and decreased levels of activity that have been reported in survivors of childhood cancer [34
The fact that besides female sex, we found no associations between demographic and personal factors and inactivity in our analysis is interesting and important. In this population, it appears that interventions targeted specifically at females and treatment related outcomes, like managing exercise with a missing or prosthetic limb, or when less than optimal sensation or motor function is available, may be more important for this population than other factors like lower household income, depression, and obesity. Sarcoma survivors may benefit from working with skilled providers who are knowledgeable and who have experience with prosthetics and movement retraining, such as physical therapists, to help them optimize physical activity levels among lower extremity sarcoma survivors before they can reintegrate into community wellness and exercise programs.
There are several limitations to this study. First, our analysis was limited to the data provided by the CCSS questionnaires and medical record abstractions. Differential participation in the 2003 questionnaire by sex and race were present. If females or those who were non-white were more likely to be inactive completed the questionnaire, our estimates of the prevalence of inactivity are inflated. Conversely, if those more likely to be inactive avoided completing the questionnaire, our estimates of the prevalence of inactivity are too low. Because our analyses were focused on discovery of personal and treatment related risks for inactivity, we did not evaluate comorbid conditions, for example, diabetes and cardiac disease, also likely to be associated with poor activity outcomes. In addition, there are potentially additional psychosocial predictors of inactivity, such as self efficacy, self motivation, or social support [22
], that were not part of the data set. Also, the study relied on self-report of physical activity. While self-report methods have been criticized, Strath et al have reported an 80% agreement between objective and self-report measures of meeting moderate and vigorous activity guidelines [36
]. Finally, these data describe individual characteristics of individuals who are at greater risk of physical inactivity but they do not provide information about perceived barriers to participation in physical activity. Such information would provide additional insights into the design of successful interventions for this population of survivors.
In summary, childhood lower-extremity sarcoma survivors are at risk for being physically inactive. This study has identified sex and treatment factors associated with these behaviors including being female, hemipelvectomy surgery, and treatment with platinum, or vinca-alkaloid chemotherapy. Interventions tailored to address these identified factors need to be developed and should consider the new CDC guidelines for children which are even more rigorous (60 minutes 7 days a week of moderate to vigorous activity - adults 30 minutes 5 times per week in addition to 2 days a week strengthening exercises) than the guidelines we used to identify outcomes in this analysis [37
]. In addition, physical activity programs should address the unique needs of lower extremity sarcoma survivors such as poor balance, peripheral neuropathy, and prosthetic or missing limbs. We hypothesize that programs designed and implemented specifically for this population of cancer survivors will be more likely to meet with success, less frustrating, and more successful in sustaining changes in physical activity levels. Such interventions will become increasingly more important as medical care for sarcoma continues to improve, resulting in more adult survivors.