Objectives To estimate the prevalence of malnutrition in elderly cancer patients and its association with frailty and primary cancer treatment recommendations in patients with the two most prevalent cancers (colorectal cancer, CRC and breast cancer, BC) in the Centre-Val de Loire region of France. Methods The entire cohort of 704 patients aged 75 years or older presenting with cancer who underwent comprehensive geriatric assessment (CGA) between 2014 and 2017 was included. Nutritional status, frailty (defined by the Balducci classification system based on CGA parameters and comorbidity), and pathological criteria were analyzed in terms of the cancer treatment recommendations suggested by geriatricians both in the whole cohort and in those with CRC and BC. Results In the whole group of 704 patients (84.3 +/- 4.8 years), the prevalence of malnutrition was 62.9％, and was higher in CRC than in BC patients (71.1％ vs 55.4％, P < 0.01). In a multivariate analysis, malnutrition and frailty (as determined by the Balducci classification system) were independently related in CRC patients (OR: 7.28, 95％CI, 1.58～34.03; P = 0.012) and were unrelated to metastasis [odds ratio (OR): 1.34, 95％CI, 0.56～3.18; P = 0.5]. By contrast, malnutrition in BC patients was related exclusively to the extent of metastasis (OR: 3.52, 95％CI, 1.50～8.24; P = 0.002). It was also demonstrated that geriatricians had a greater tendency to suggest only palliative care to CRC patients presenting with malnutrition (15.4％ vs 2.7％, P = 0.006) than to BC patients (9.8％ vs 5.4％, NS). Conclusion Malnutrition in elderly cancer patients is prevalent, especially in those with colorectal cancer, where malnutrition is frailty-related and may strongly impact on cancer treatment strategies.