Background: This thesis evaluates the impact of geriatrician-delivered comprehensive geriatric assessment (CGA) interventions on chemotherapy toxicity and tolerance for older people with cancer. While comorbidities are identified in routine oncology practice, intervention plans for the co-existing needs of older people receiving chemotherapy are rarely made and have rarely been evaluated. Methods: Comparative study of two cohorts of older patients (aged 70+) undergoing chemotherapy in a London Hospital. The observational control group (N=70, October 2010 - July 2012) received standard oncology care. The intervention group (N=65, September 2011 - February 2013) underwent risk stratification using a patient-completed screening questionnaire; high risk patients received CGA. Impact of CGA interventions on chemotherapy tolerance outcomes and grade 3+ toxicity rate were evaluated. Outcomes were adjusted for age, comorbidity, metastatic disease and initial dose reductions. Results: Intervention participants undergoing CGA received a mean of 6.2+/-2.6 (range 0-15) CGA-based interventions. They were more likely to complete cancer treatment as planned (odds ratio (OR) 4.14 (95% CI 1.50-11.42), p=0.006) and fewer required treatment modifications (OR 0.34 (95% CI 0.16-0.73), p=0.006). Overall grade 3+ toxicity rate was 43.8% in the intervention group, 52.9% in the control (p=0.292). Conclusions: Geriatrician-led CGA identified many indications for interventions. This approach was associated with improved chemotherapy tolerance. Embedding CGA interventions in oncology practice merits further evaluation.