Ce2PtIn8 is a recently discovered heavy-fermion system structurally related to the well-studied superconductor CeCoIn5. Here we report on lowerature de Haas-van Alphen-effect measurements in high magnetic fields in Ce2PtIn8 and Pr2PtIn8. In addition, we performed band-structure calculations for localized and itinerant Ce-4f electrons in Ce2PtIn8. Comparison with the experimental data of Ce2PtIn8 and of the 4f-localized Pr2PtIn8 suggests the itinerant character of the Ce-4f electrons. This conclusion is further supported by the observation of effective masses in Ce2PtIn8, which are strongly enhanced with up to 26 bare electron masses.