There are several ways to tell if a tumor is responding to treatment. They are pretty much the same methods used to diagnose the tumor in the first place—physical examination, x-rays, blood tests and scans. These same tests will have been done before treatment to establish a baseline for future comparisons.
• A lump or a tumor involving lymph nodes can be felt and measured directly. The size of the liver, spleen and
  other organs can also often be determined by physical examination. Your doctor will record these direct
  measurements in your chart and compare them from time to time to see if the size of the tumor is decreasing.
• Some tumors, such as those involving the lungs, show up on x-rays. If new x-rays are taken at one-, two- or
  three- month intervals, the size of the tumors on the x-ray film can be measured directly with a ruler.
• Internal tumors, such as those involving the liver or other organs, are more difficult to measure. So special
  techniques have to be used—scanning using radioactive tracer isotopes, CT or MRI. Again, the size of the
  tumor as shown on the image can be measured directly at various intervals.
• Sometimes blood tests provide a clue to tumor response. Both non-specific tests, such as liver function tests ,
  and tests for specific tumor markers may be used.