Epidemiologic Studies of Social Factors to Promote Quality of Life and Survival in Prostate Cancer Survivors

Abstract

Prostate cancer is the leading cause of cancer incidence in over 100 countries, with over 1.5 million new cases diagnosed yearly across the globe. There are many individuals who live for many years, or even decades, beyond their prostate cancer diagnosis. In the United States alone, there are an estimated 3.6 million prostate cancer survivors, over 180,000 of whom living with metastatic disease. With screening, aging of the population, and treatment advancements allowing individuals to live longer beyond their diagnosis, the population of prostate cancer survivors is expected to continue to grow. As such, the survivorship period is an especially important part of the cancer control continuum in the context of prostate cancer. Living longer does not necessarily mean that individuals are living well, so finding opportunities to optimize prostate cancer survivorship is an important direction of public health research that stands to benefit a large and growing population. In Chapter 1, we provided a broad overview of the literature that informed this body of work on prostate cancer survivorship. Specifically, we described the burden of prostate cancer and the importance of studying survivorship for this patient population. In addition, we highlighted the potential role of social factors in influencing outcomes during prostate cancer survivorship, which motivated the work presented in subsequent chapters. In Chapter 2, we examined the cross-sectional and longitudinal associations between the level of caregiving-related burden of informal caregivers and the quality of life (QoL) of prostate cancer survivors receiving their care, in 307 dyads of Black prostate cancer survivors and their primary caregivers enrolled in the Detroit Research on Cancer Survivors (ROCS) cohort. We observed significantly higher QoL scores, particularly in physical and functioning QoL domains, among survivors whose caregivers perceived low burden, compared to those whose caregivers perceived higher levels of burden. When we additionally factored in information on objective metrics of burden (e.g., amount of time providing care weekly), we observed the highest QoL scores among survivors whose caregivers perceived low burden and had low levels of objective burden. While the causal nature of the relationship between caregiver burden and survivor QoL cannot be comprehensively determined in this study, the findings motivate future investigations in larger cohorts with clearer temporality in measurement. In summary, the findings suggest that both perceived and objective caregiving-related burden influence the wellbeing of prostate cancer survivors. In Chapter 3, we considered the role of an informal caregiver’s own health-related wellbeing on QoL outcomes in prostate cancer survivor care recipients in 298 dyads in Detroit ROCS. Using a latent class analysis-derived measure of caregiver wellbeing, we found that the baseline QoL of cancer survivors was higher, on average, in those whose caregivers had higher levels of both psychological and physical wellbeing, compared to lower wellbeing in both domains. Taken together, the findings from Chapters 2 and 3 highlight the roles that the burden and wellbeing of informal caregivers can play in influencing outcomes among those receiving their care. Given the prevalence of informal cancer caregiving, this relationship, if it is robust, has important implications for considering caregivers in cancer clinical care plans. In Chapter 4, we examined the relationship between social integration, a multi-faceted metric of structural social connectedness, and mortality attributable to the major causes of death in over 5,600 prostate cancer survivors with a median of 21 years of follow-up in the Health Professionals Follow-up Study. We observed significantly lower hazard rates of prostate cancer-specific mortality in highly socially integrated, compared to socially isolated, prostate cancer survivors. Marital status was a single component of social integration found to be independently related to mortality. This study contributes one of the first investigations into the role of social integration on mortality in prostate cancer survivors, with findings highlighting the long-term benefits of social connectedness during survivorship. In Chapter 5, we described unique patterns across 17 functioning and symptom domains of health-related quality of life (HRQoL) in a sample of over 3,600 advanced prostate cancer survivors from 12 countries. Four patterns emerged. The most prevalent HRQoL pattern, assigned to nearly half of the population, was that determined to reflecting thriving in survivorship, in which individuals were most likely to have excellent HRQoL in every domain assessed. The remaining patterns reflected Good HRQoL, Fair HRQoL, and Poor HRQoL, the latter of which was the least prevalent but represented higher likelihood of having poor role functioning, fatigue, pain, sleep, financial wellbeing, and overall health status. Following the population for 5.5 years, we observed a nearly 3-fold higher risk of mortality in patients assigned to the Poor HRQoL pattern, compared to the Thriving pattern. This study demonstrated how poorer wellbeing in specific domains may cluster together and synergistically influence outcomes in advanced prostate cancer survivorship, informing possible specific targets for monitoring and intervention in an effort to offset the significant mortality risk associated with the pattern. In summation, this thesis has highlighted unique experiences of prostate cancer survivorship in three distinct patient populations captured within robust epidemiologic cohorts. Conclusions across the chapters is provided in Chapter 6. As more patients are living for many years beyond their prostate cancer diagnosis, finding opportunities to optimize survivorship can have important public health impacts on this large and growing population of prostate cancer survivors.