Introduction of chemotherapy

This topic will discuss role, selection and length of chemotherapy in treating cancer. And understanding the mechanism of chemotherapy drugs..
Abdelwahab Ward, BS Pharm, PharmD
This article was written by: Alaa Khalid Said, BS Pharm, PharmD.
  • Senior oncology pharmacist,
    Clinical Pharmacy Department, Tanta Oncology Center.

OVERVIEW ã…¡ Chemotherapy is the use of drugs to destroy cancer cells. It usually works by keeping the cancer cells from growing, dividing, and making more cells. As cancer cells are growing and dividing more fast that the normal cells, chemotherapy is more effective on cancer cells. However, chemotherapy drugs are powerful and can still damage the normal healthy cells.

    CELL CYCLE

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    Figure (1)
    Understanding cell cycles.

    To understand the mechanism of chemotherapy drugs, we have to understand the cell cycles ã…¡ see, Figure 1.

    • G0 phase (resting stage): the cell is at rest and has not started to divide. This can last for a few hours to a few years, depending on the circumstances (reproductive cells have a very short resting phase whereas plant seeds have been known to germinate many years after they have been deposited).
    • G1 phase: the cell starts to make more proteins and is ready to divide. This usually lasts 18–30 hours.
    • S phase: the DNA chains are copied so that the new cell has the same DNA. This usually lasts 18–20 hours
    • G2 phase: this is just before the cell starts splitting into two cells. This phase usually lasts from 2–10 hours.
    • M phase: the cell splits into two new cells. This phase usually lasts 30–60 minutes.
    Some chemotherapy medicines can kill a cell during any phase of the cell cycle. They are called cell-cycle nonspecific agents. Other chemotherapy medicines kill cancer cells only during a certain phase. They are also not able to work in the resting phase. These are called cell-cycle specific agents.

    CHEMOTHERAPY TREATMENT

    Doctors use chemotherapy in different ways at different times. These include...
    • Before surgery or radiation therapy to shrink tumors. This is called neoadjuvant chemotherapy.
    • After surgery or radiation therapy to destroy any remaining cancer cells. This is called adjuvant chemotherapy.
    • As the only treatment. For example, to treat cancers of the blood or lymphatic system, such as leukemia and lymphoma.
    • For cancer that comes back after treatment, called recurrent cancer.
    • For cancer that has spread to other parts of the body, called metastatic cancer.

    GOAL OF CHEMOTHERAPY

    The goals of chemotherapy depend on the type of cancer and how far it has spread. Sometimes, the goal of treatment is to get rid of all the cancer and keep it from coming back. If this is not possible,the goal become to delay or slow cancer growth. Delaying or slowing cancer growth with chemotherapy also helps manage symptoms caused by the cancer. Chemotherapy given with the goal of delaying cancer growth is sometimes called palliative chemotherapy.

    CHEMOTHERAPY DRUG SELECTION

    The drugs, dose, and treatment schedule depend on many factors. These include...
    • The type of cancer.
    • The tumor size, its location, and if or where it has spread. This is called the stage of cancer.
    • Your age and general health.
    • How well you can cope with certain side effects.
    • Any other medical conditions you have.
    • Previous cancer treatments.

    LENGTH OF CHEMOTHERAPY

    Chemotherapy is often given for a specific time, such as 6 months or a year. Or you might receive chemotherapy for as long as it works. Side effects from many chemotherapy drugs are too severe to give treatment every day. So, doctors usually give these drugs with breaks, giving patient time to rest and recover before the next treatment and chance for healthy cells to heal. Some cancers are treated with less recovery time between cycles. This is called a dose-dense schedule. It can make chemotherapy more effective against some cancers. But it also increases the risk of side effects from it.

    REFERENCES

    Abdelwahab Ward, BS Pharm, PharmD