By placing side-by-side two ongoing studies based on interventional research dynamics in the field of cancer, this article considers the specific effects of this type of research. Although this approach is often poorly regarded in the field of academic sociology, it is particularly suited to the analysis of ongoing processes, providing access to certain phenomena that would otherwise be impossible to observe. The research worker’s active involvement, the experience that he/she shares with the subjects studied and the partnerships formed with institutional bodies give rise to the production of original scientific knowledge; but they can sometimes also create uncomfortable situations.