Why to do chemotherapy if cancer cells can still be left behind for reccrrence after the treatment? doesn;t chemo kill all the cells?

Cure is our goal...: Some people can be completely cured of their cancer using chemotherapy, while others eventually relapse and their cancer comes back. Our goal with chemotherapy is to rid the body of all cancer cells, but sometimes this doesn't work. We are not that good at predicting upfront who will be cured and who will relapse, so that is why we try and see what happens. This is an area of intense research.

Statistics: Rx is based on the average response of large populations. Unfortunately, we cannot individualize rx to the point where we can predict success with 100% certainty. Also, since the disease is often microscopic, we cannot always measure the response. Therefore, the best we can offer is that the odds are in your favor.

Cancer cells: That is the million dollar question! adjuvant chemo is suppose to eradicate or kill the micrometastasis increasing the curative potential. It can do that in majority of patients but not in every one. Cancer cells find ways of survival by hijacking the host immune system, by affecting the microenvironment, and by changing their phenotype into stem cell type, a phenomenon called emt they outsmart us.