This chapter originally started life as applications in clinical medicine and as such it would have been relatively easy to write five years ago. However, with the amazing proliferation of flow cytometry applications in medicine during the past few years this has become such a daunting prospect that I ‘ducked-out’ and decided to contract it to applications in clinical oncology. The latter discipline in the UK means all aspects of cancer patient management including diagnosis, pathology, surgery, radiation therapy and drug treatment. Writing in my capacity as a clinical oncologist I think I can cope with this, but I would like to stress the ‘think’, as this is still a formidable undertaking. At this point I would advise people who have no interest in cancer and whose area has not been covered to move smartly on to the epilogue where you may find just a brief mention of your field which has been omitted from the volume. However, I suppose that won't help much so you might as well stop here.

After further deliberation I decided not to embark on a comprehensive account of all that has been done in cancer with flow cytometry although many of the references are included. I thought it might be more constructive to try to concentrate on what needs to be done and how flow cytometry might be able to help. In order to effect this approach it is necessary to ask a number of questions although I'm not trying to pretend there are any ‘real’ answers at present.