test of a patient's tumor cells would not usually be used with that patient.
      These tests may be useful in selected patients, but are not yet the final solution to the problem of drug
  selection. Their usefulness is limited by a number of factors:
• The tumor may not grow in the laboratory, or only certain drug-sensitive cells may grow.
• There may be differences between the way the drug works in the body and the way it works in a test tube. In
  the body, the drug can be bound and inactivated, eliminated by the kidneys or not be allowed to get through
  the P-glycoprotein "gate" on the cell surface.
• These test procedures apply only to one or, at most, two drugs tested one at a time. But chemotherapy cures
  are generally produced only by combinations of many drugs.
• The possibility of using other therapies There is no one absolutely right choice in cancer therapy, and the
  treatments recommended can change over the course of the illness. One reasonable choice at a particular time
  may not be appropriate at a later time.
      A woman whose breast cancer recurs in a non-vital place, for example, may have several options. Her
  doctor may recommend: surgery, radiation treatment to the region to possibly control the cancer for years,
  hormone treatments, simple chemotherapy, complex chemotherapy or even doing nothing until the cancer
  grows and starts to bother her in six months' or a year's time.
      Each treatment option has advantages and disadvantages, and there may be more than one option that is
  sensible.