Large-scale evidence on colorectal cancer survivorship: relationship of colorectal cancer diagnosis to physical functioning limitations and psychological distress over time
Creators: name: Zhang, Yuehan
Publisher: name: The Australian National University
Year: 2021

description: Colorectal cancer (CRC) is the third most common cancer in Australia. It has a 70% 5-year survival rate; hence, most people with CRC now survive long-term. Evidence on physical and psychological outcomes among individuals with CRC is critical to providing appropriate guidance to survivors and those caring for them. However, reliable evidence on such outcomes over time, especially compared to the general population, is lacking. This thesis used data from the 45 and Up Study questionnaires linked to cancer registry and hospital admissions data, and aimed to quantify: (i) physical disability and psychological distress in people with and without CRC; (ii) the role of comorbidity in the relationship of CRC to adverse outcomes; and (iii) changes in outcomes before and after CRC, compared to people without cancer, over a similar time period. To address the first aim, I investigated physical disability and psychological distress in people with and without CRC, and the joint relationship of CRC and physical functioning to psychological distress. This study included 213,231 participants, among whom 2,395 had CRC. Overall, physical disability was more prevalent in people with versus without CRC, and psychological distress was similar between two groups. Long-term survivors, those with less advanced disease, and those without recent treatment had outcomes similar to the general population. Disability and distress were elevated in survivors with recent diagnosis and treatment and those with advanced disease. The risk of psychological distress was four-to-five times higher in people with versus without physical disability, regardless of CRC status. To address the second aim, I investigated the joint relationship of CRC and comorbidity to adverse outcomes, and assessed the extent to which CRC-outcomes associations varied according to comorbidity. Using the same study population as above, I considered six comorbidities. People with comorbidity, especially multimorbidity, experienced more adverse outcomes than people without comorbidity, regardless of CRC status. Comorbidity did not attenuate CRC-disability associations, meaning CRC itself is the most likely explanation for increased physical disability in CRC survivors. To address the third aim, I investigated the changes in outcomes among CRC survivors before and after diagnosis, compared to people without cancer over a similar time period, and the joint contribution of CRC and changes in physical functioning and psychological distress. This study included 93,930 participants with baseline and follow-up questionnaires, among whom 546 were diagnosed with CRC between two questionnaires. Physical functioning decreased more in survivors following diagnosis, than in people without cancer over time. CRC did not materially affect the level of psychological distress experienced. People with physical deterioration, regardless of whether or not they had CRC, had markedly worsening psychological distress than those whose physical functioning remained constant. I also investigated the role of missing outcome data largely due to non-completion of follow-up questionnaire; I found no evidence that it materially affected findings compared to complete-case analyses. The evidence generated in this thesis indicates that CRC survivors experience a decrease in physical functioning following diagnosis and are generally more likely to experience disability than the general population. Survivors can be reassured that, in the long term, levels of psychological distress in those with CRC are generally similar to the broader population, especially if they have fewer limitations in physical functioning.