Background. The GP’s role in cancer care is changing and will become increasingly important. One of the challenges for GPs in caring for cancer patients is their lack of specialized knowledge and the impossibility to keep up to date with developments in the field of oncology. We investigated GPs use of knowledge in the case of the increasing use of oral anticancer therapy at home. Objective. The objective of the study was to find out the needs for knowledge improvement for GPs in caring for cancer patients at home, by analysing what kinds of knowledge Dutch GPs use and the ways they obtain knowledge in their daily practice of caring for patients using oral anticancer therapy at home. Methods. Semi-structured in-depth interviews were conducted between July and November 2011 with 15 Dutch GPs. A thematic analysis of interview transcripts was conducted. Results. GPs recognize their lack of specialized knowledge and their inability to keep up to date with developments in the field of oncology. The analysis shows that GPs use different kinds of knowledge and skills they already have to care for their patients and obtain valuable knowledge about oral anticancer therapy via and from their patients. Conclusion. Apart from formal training, GPs may be supported to strengthen the strategies they already use, i.e. to actively mobilize different types and sources of knowledge and use the patient as a source of knowledge in caring for oncology patients at home.