The treatment of cancer through the twentieth century may be seen as the successive addition of modalities: first surgery; then radiotherapy, especially between the world wars; and then chemotherapy, from the 1960s. This paper explores some of the systematic differences between the modalities, and how these additions were negotiated in different countries, with different long-term consequences for the development of services and specialization. It focuses chiefly on the United Kingdom and the United States, the former exemplifying a centralized health polity, and the latter, liberal markets combined with large and crucial postwar inputs from government. The differences between health polities were especially important for interwar radiotherapy, which in its centralized form appeared as paradigmatic of the analytical/rationalizing mode in modern medicine. Chemotherapy exemplified a more inventive and experimentalist mode that became common after World War II, and that, through the practice of trials, shaped the new subprofession of medical oncology. The interactions of the modalities, at various levels, are modeled as contested cumulations showing strong path dependency. The paper ends by reviewing the present situation, especially for Britain, and by underlining the relevance of history.