The decision and determinants of adjuvant chemotherapy for stage III colon cancer

Hassan, Syreen (2022) The decision and determinants of adjuvant chemotherapy for stage III colon cancer. PhD thesis, Birkbeck, University of London.

Abstract

Introduction: Treatment of stage III colon cancer consists of surgery to remove the tumour followed by ‘adjuvant’ chemotherapy, which serves to eradicate the microscopic cancer cells that cannot be removed by surgery. Adjuvant chemotherapy could include therapy with a single agent (a fluoropyrimidine) or in combination with a second medication, known as oxaliplatin. Oxaliplatin offers an additional absolute increase of 3-4% in five-year overall survival and 6-7% in five-year disease-free survival. However, it can also result in a condition called peripheral neuropathy (PN), which can persist and influence quality of life. There is no effective prevention or treatment of PN. Therefore, a modest improvement in survival needs to be balanced against a potential risk of persistent neurotoxicity. The focus of this thesis was onstage III colon cancer, to allow for an understanding of the factors that could influence treatment in a setting where the treatment decision is relatively simple. By contrast, settings where more complicated therapy, such as radiotherapy or neo-adjuvant chemotherapy for rectal cancers, may be required adds to the complexity of the decision-making process and the trade-offs to be considered. Objectives and methods: Four studies were under taken to investigate determinants of adjuvant chemotherapy among this population of patients. First, a systematic review of the literature to determine the prevalence of PN resulting from treatment with oxaliplatin. Second, secondary data analysis to investigate the role of patients’ sex, age, ethnicity, socioeconomic status, and tumour characteristics as determinants of adjuvant chemotherapy and type of chemotherapy received. Third, a qualitative study to investigate how the decision to receive adjuvant chemotherapy and the choice of the type of therapy was made, the nature of the patient-clinician interaction, and what contextual elements may have influenced this interaction. Fourth, a secondary analysis of questions from the National Cancer Patient Experience Survey (NCPES) to determine the extent to which patients perceived being informed about treatment options and side effects, as well as being involved in the treatment decision. Results: PN is likely to persist among 40% of patients at six months, and between 25-30% at twelve months or longer. Those of older age, of minority ethnic groups, and of lower socioeconomic status were less likely to receive combination therapy than those who were of younger age, White ethnicity, or higher socioeconomic status. Most participants in the qualitative study lacked awareness of treatment options and side effects and did not participate in a decision-making process with the clinician to decide on which treatment to receive. The NCPES showed that those who received combination chemotherapy were less likely to be certain when asked whether they knew about side effects and future side effects of treatment compared to those who received single therapy. Conclusion: the decision to receive oxaliplatin for the treatment of stage III colon cancer does not occur through a shared decision-making process. Patients who receive combination chemotherapy are in adequately aware and informed of the likelihood and nature of peripheral neuropathy, which could persist in more than a quarter of patients at least one year after treatment. Group-level variations in the receipt of combination therapy indicates systemic-level inequalities in treatment. A shared decision-making process could increase patients’ awareness of their treatment options and side effects and reduce the inequalities that result from provider biases and system-level factors.

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