treating breast cancer early on the most common treatment for breast cancer Was the removal of breast it is now usual for the to remove only the tumor and nearby lymph nodes followed by radiation. the change in policy was due to a large medical experiment that compare the two treatments. is some breast cancer patients chosen at random we're giving one or the other treatment period the patient was closely followed to see how long they lived following the surgery. What are the explanatory and response variables? Are they categorical or quantitative?