There is an increased focus on supporting patients with cancer to actively participate in their healthcare, an approach commonly termed ‘self-management’. Comparing unmet self-management needs across cancer types may reveal opportunities to adapt effective self-management support strategies from one cancer type to another. Given that breast and colorectal cancers are prevalent, and have high survival rates, we compared these patients’ recent need for help with self-management. Data on multiple aspects of self-management were collected from 717 patients with breast cancer and 336 patients with colorectal cancer attending one of 13 Australian medical oncology treatment centres. There was no significant difference between the proportion of patients with breast or colorectal cancer who reported a need for help with at least one aspect of self-management. Patients with breast cancer were significantly more likely to report needing help with exercising more, while patients with colorectal cancer were more likely to report needing help with reducing alcohol consumption. When controlling for treatment centre, patients who were younger, experiencing distress or had not received chemotherapy were more likely to report needing help with at least one aspect of self-management. A substantial minority of patients reported an unmet need for self-management support. This indicates that high-quality intervention research is needed to identify effective self-management support strategies, as well as implementation trials to identify approaches to translating these strategies into practice. Future research should continue to explore whether self-management support strategies could be adapted across cancer types.