Chemotherapy: Duration of the Treatment

The duration of chemotherapy treatment depends on several factors, including the histological type and stage of mesothelioma, the class of drugs being administered, toxicities associated with the drugs, and the time needed to recover from those toxicities. The medical community derives chemotherapy treatment schedules (the specific types and their duration) from experience and from clinical trials. These trials compare treatment schedules to determine which ones offered the most benefits and are easily tolerated.

The objective of a chemotherapy treatment cycle design is to attack cancer cells at a time when they are most susceptible and also provide time for the normal cells in the body to recover from the adverse affects of chemotherapy. Cycle time involves three major issues – duration of the cycle, its frequency and the total number of cycles.

Duration of the cycle: During chemotherapy treatment, either a single drug or a combination of drugs is used. The treatment may require all the drugs to be administered on a single day, or on successive days, or continuously on an outpatient or inpatient basis. Administration of the agents can last minutes, hours or days.

Frequency of the cycle: The frequency of chemotherapy treatment may be weekly, bi-weekly or monthly. Often, a cycle is determined based on monthly intervals. For instance, two or more bi-weekly chemotherapy sessions can be treated as a single cycle.

Number of cycles: In a majority of treatment protocols, the number of cycles (or the overall duration of the treatment from beginning to end) has been established through research and clinical trials.

  • When the treatment targets cure, adjuvant chemotherapy (therapy administered after surgery has destroyed all detected cancer) can last 4-6 months or more.
  • When the disease is clearly visible, the duration of chemotherapy treatment depends on how the cancer responds to the therapy. If the disease is cured completely, the treatment may be administered for 1-2 cycles beyond this point to increase the probability of having targeted all microscopic disease.
  • If the tumor reduces in size, but is not cured completely, chemotherapy will continue to be administered, given that it is tolerated and the tumor does not start to grow.
  • If the disease continues to grow, doctors will stop administering chemotherapy. Depending on the patient’s health and wishes, either a combination of drugs will be administered to treat the cancer, or treatment will be stopped completely and focus will shift to patient comfort.

How Do We Know if Chemotherapy is Working?

Other than the exception of adjuvant chemotherapy wherein no visible disease is present, the effect of chemotherapy on malignant cells is measured on the basis of “response”. The techniques that are used for measuring responses are similar to those utilized for cancer diagnosis.

  • The doctor can carry out a physical examination to feel and measure a lump or tumor that involves specific lymph nodes.
  • X-ray or CT scans can reveal specific types of internal cancer tumors that can be measured using a ruler.
  • Blood tests can be performed, for example, tests that can measure organ function.
  • Clinical tests involving tumor markers can also be carried out.

Irrespective of the type of test performed (be it cell count, tumor marker test, or cell count), it is repeated at regular intervals in order to allow doctors to compare new test results with earlier ones.

How is response defined?

Response to cancer treatment can be described in the following ways:

  • Complete response: There are no visible signs of tumor or cancer; there is no evidence to suggest the presence of the disease. If applicable, a tumor marker will display the normal range.
  • Partial response: The cancer has reduced by a specific percentage, but the disease remains. A tumor marker may have failed, but still evidence of the disease remains.
  • Stable disease: There is neither reduction nor growth in the cancer; the quantum of disease remains unchanged. If applicable, a tumor marker does not display significant change.
  • Disease Progression: The cancer has increased; there is more of the disease now in comparison to the pre-treatment stage. If applicable, a tumor marker test will indicate that the cancer has progressed.

When is response measured?

The number of treatments is fixed for individuals who have been newly diagnosed and have been prescribed chemotherapy. For instance, an oncologist can prescribe a fixed number of chemotherapy cycles according to the treatment protocol. Responses can be assessed and reviewed during the treatment, but the number of prescribed cycles does not usually change unless there are indications of a progression in disease. In case the cancer grows, either chemotherapy will be stopped or different drug combinations will be used.

However, a fixed number of treatment cycles may not be applicable to patients with advanced disease or those experiencing a relapse. Instead, treatment is carried out for 2-3 cycles, after which the response is measured. If the disease has stabilized or shrunk, more of chemotherapy can be performed, provided that responses are maintained and toxicities are within tolerable levels. Generally, at least 2-3 treatment cycles are required to measure a response. A single cycle of chemotherapy treatment may not be enough to measure its effectiveness.

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