Timing Cancer Treatment

Lung Cancer
Lung cancer is the second most commonly diagnosed cancer among American men and women and the leading cause of cancer death. This year, the American Cancer Society estimates 171,900 new cases will be diagnosed in the U.S. About 157,200 will die from the cancer.

The most important risk factor for lung cancer is smoking. About 87 percent of the cancers can be attributed to direct (active smoking) or indirect (passive smoking) exposure to tobacco smoke. The longer a person smokes and the more cigarettes smoked/day, the greater the risk for lung cancer. People who work with or are exposed to asbestos are seven times more likely to die from lung cancer. Asbestos workers who smoke have 50 to 90 times the risk of developing the cancer. Exposure to radon (a gaseous byproduct of uranium breakdown) is also associated with an increased incidence of lung cancer. Other potential risk factors include: use of marijuana (which contains more tar than cigarettes), exposure to certain chemicals in the workplace, recurrent lung inflammation, personal or family history of lung cancer and air pollution.

Treating Lung Cancer
When lung cancer is diagnosed, doctors may try to surgically remove the tumor and a small area of surrounding healthy tissue. Partial removal of a lung lobe (section of the lung) is a segmentectomy or wedge resection. Removal of the whole lobe is a lobectomy. A pneumonectomy is the removal of the entire lung. Radiation therapy may be given to destroy cancer cells. Chemotherapy is treatment with anticancer drugs. Patients often receive more than one type of treatment in an attempt to destroy or control the cancer.

Overall, the average one-year survival rate for lung cancer patients is about 42 percent. Five-year survival rates are only about 15 percent. The reason for poor survival is that most patients don't develop any symptoms until the disease has advanced. Only about 15 percent of patients are diagnosed while the disease is still localized, when five-year survival rates are about 49 percent.

Timing Treatment for Lung Cancer
Cancer cells grow and divide in a very orderly process involving four stages. GAP 1 (G1) is the beginning stage in the cell cycle. During this stage, the cancer cell grows in size and produces proteins needed for DNA replication. The cell then moves into the second phase, called Synthesis, or the S-phase. During this phase, the cell makes a copy of its DNA, which sets the stage for division into two separate cells. But before the cell can divide, it must continue to grow and produce more proteins. This third phase is the GAP 2, or G2 phase. The last phase of the cell cycle is mitosis, or the M phase. The cell splits apart into two daughter cells, with each daughter cell ready to begin the cell cycle anew. Cancer cells typically complete a growth cycle in 24 to 48 hours.

Cancer cells are most susceptible to radiation when they are transitioning from the G2 to the M phase of the cell cycle (the time frame referred to as the G2 M phase). However, cancer cells don't follow the exact same cycle. At any given time, some cells may be in the G1 phase, some in the S phase, some in the G2 phase and some in the M phase. Thus, even over a series of treatments, radiation may not effectively target all the cancer cells.

Researchers at the University of Rochester are studying a treatment regimen that takes advantage of the cancer cells' susceptibility to radiation during the G2 M phase of the cycle. Lung cancer patients received low doses of the chemotherapy drug, paclitaxel on Mondays, Wednesdays and Fridays before 11:00 AM. Paclitaxel causes cancer cells to remain in the G2 M phase of the cell cycle (when the cell is most sensitive to radiation). Five hours after chemotherapy, patients received radiation therapy. Radiation was also given on Tuesdays and Thursdays.

Thirty-three participants completed Phase I of the trial. Investigators found 100 percent of the tumors responded to the treatment. In 98 percent of patients the tumor shrank or disappeared. Doctors say the treatment regimen needs further study to verify its effectiveness and safety. However, the low dose of chemotherapy combined with timed radiation appears to be much less toxic than standard chemo/radiation regimens. That would make the new therapy safer and more tolerable for older patients and those who are too sick to undergo standard lung cancer treatments.

For general information on lung cancer:
American Cancer Society, contact your local chapter, or visit their website at http://www.cancer.org
National Cancer Institute, http://www.nci.nih.gov