Question on how to cure cancer?

If chemotherapy destroys rapid growing cells including the good ones like blood and hair why cant they use this solution. Step 1 draw the blood from the patient showing the good healthy cells and the bad cancerous cells. step 2 somehow make the chemotherapy recognize the good cells and the bad cells. step 3 once they somehow make the chemo recognize these cells put that solution inside the patient making most of the side effects go away and extending the patients life instead of just living for about 5 or 6 years. i have always thought of this and never really knew an answer. I know its not as easy as it sounds but this keeps popping up in my mind.