Cancer Treatment
We’ve seen what cancer is and what we think causes it. What about cancer treatment? How do we treat and cure this fearsome disease? There are three ways to treat cancer: surgery, radiation and chemotherapy. Surgery is by far the most common cancer treatment. Removal of a tumor that is localized can cure cancer. Much of cancer surgery in recent years has become conservative of the surrounding tissue.
Radiation is used in cancer treatment on localized regions that can’t be removed in surgery. This might be in a very diffuse area, for example. It also might be useful to shrink a tumor that is up against a vital organ and the surgeon is afraid of damaging that organ. Radiation damages DNA, it causes both strands of DNA to be broken. The amounts of radiation used are small from the military viewpoint, but quite large from the medical one. Let’s illustrate this. The lifetime exposure to radiation of a typical person on Earth is about 0.12 gray (a physical unit). During the course of radiation treatment, the tumor itself gets 50 gray over five weeks. That’s 400 times the lifetime dose.
The third method of cancer treatment is called chemotherapy. It is used when tumors have spread over the body, because when you put a drug in the blood system, it will be distributed everywhere. Typical chemotherapy uses drugs that kill all dividing cells, including the tumor. There are side effects to chemotherapy. Normal tissues get affected, like bone marrow, cells in the intestines and skin.
A wide array of drugs that block cell division have been isolated and are used. Some are natural products we get from plants, others we build in the laboratory.
A Real Life Case
This is a real case involving cancer treatment with chemotherapy. John first noted that he tired easily at the gym. It got worst over several weeks. When he began to have shortness of breath even when he walked from room to room, he decided to see his physician. When his doctor looked at a drop of blood under the microscope, he saw many white blood cells. A blood sample was sent to laboratory, and they confirmed that he had over 200000 white blood cells per milliliter. This is 40 times normal. An hematologist looked at bone marrow as well as the blood and found a lot of immature white blood cells. In addition, he saw an abnormality: a funny looking chromosome called the “Philadelphia chromosome”. The diagnosis: chronic myelogenous leukemia.
No one knows how, but in this disease, the DNA in two chromosomes inside an immature white blood cell is cut and spliced. Two chromosomes exchange material, so that part of two genes that are ordinarily on separate chromosomes come to be right beside one another. The shuffled chromosome that was seen in John’s white blood cells was first noticed by scientists in Philadelphia in 1960, that’s where it got its name. White blood cells carrying this strange chromosome are stimulated to divide very rapidly. This is why they found this huge number of cells in John.
John was first treated with standard chemotherapy. He was given drugs designed to kill any reproducing cell. One of the drugs bound to DNA. A second one blocked the assembly of amino-acids. A third drug blocked the mechanism that partitions chromosomes to new cells. These drugs have bad side effects on other dividing cells. Using this conventional cancer treatment, John’s white blood cell count went down from 200000 per milliliter to 80000 per milliliter. This is still 16 times normal, however.
The drugs that John took blocked cell division all over the body. They were non-specific. John’s oncologist now tried a new approach: a specific drug. In the 1990’s, the molecular biology of this type of leukemia was described in detail. The new gene found in the Philadelphia chromosome was sequenced, and its protein product was studied. The protein turned out to be a terrific cell-division stimulant. It causes cells to divide without control.
Next, chemists at a drug company went into the laboratory and designed a brand new substance: a chemical that would specifically bind to and inactivate this new gene product in the tumor cells. At the University of Oregon, Dr. Brian Druker coordinated a clinical trial in which patients with chronic myelogenous leukemia were given this drug; to test for its safety and then its effectiveness. Patients like John, whose blood concentration of white blood cells was still high, were given the new drug and the result was spectacular. In John’s case, his white blood cell count went down to a normal 5400 per milliliter. He was cured.
The development of this drug, which is called Gleevec, is a great example of a new molecular approach to cancer treatment. The aim is to find out precisely what’s going wrong in a tumor cell and design rational treatments on this basis.
Precise molecular descriptions of the chemical biology of cancer are leading to new drug treatment for cancer and targeted chemotherapies.
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