Chemotherapy

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Chapter 39 Chemotherapy

Chapter contents

History 307

Uses of chemotherapy 307

The cell cycle 307

The aims of chemotherapy treatment 308

Terminology 308

Major groups of cancer 309

Chemotherapeutic agents 309

Chemotherapy is used in treatment of cancer. There are two types of chemotherapy:

• antineoplastic: anticancer

• cytotoxic: kills the cells.

History

The treatment of cancer by chemotherapy started in the 1940s after military personnel were accidentally exposed to mustard gas. Examination of their blood showed abnormally low white cell counts and it was thought that this might have an effect on patients with cancer. It was tried out on patients with advanced lymphomas and given intravenously. Their improvement, although temporary, was enough to start research into chemotherapy.

Uses of Chemotherapy

Chemotherapy is a systemic treatment and is therefore used when the cancer has spread to various sites in the body. Radiation and surgery are used when the problem is localized.

The Cell Cycle

To understand how chemotherapy works it is necessary to understand the lifecycle of a cell (Figure 39.1):

• 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). The cell becomes activated.

• G1 phase: the cell starts to make more proteins and is ready to divide. This usually lasts 18–30 hours.

• S phase: the deoxyribonucleic acid (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.

Figure 39.1 The phases of the cell cycle.

Chemotherapy works on actively reproducing cells. Different drugs act on different parts of the cycle. Oncologists use different groups of drugs to act on certain parts of the cycle. The problem with chemotherapy, however, is that it also acts on normal cells that are actively reproducing. The reproductive cells tend to be the ones that are most badly affected as they are multiplying relatively rapidly. The trick is to balance killing off too many good cells along with the bad cells.

The Aims of Chemotherapy Treatment

There are three aims.

• Cure: so the cancer does not return.

• Control: stopping the disease spreading and try to provide quality of life while the patient is alive.

• Palliative: if the cancer is in an advanced stage drugs are used to relieve the symptoms, even though they might not increase the patient’s life span.

Terminology

• Adjuvant therapy: postsurgical treatment to prevent the growth of any remaining cells and metastasis around the body.

• Benign tumour: remains confined to original location. There is no invasion of surrounding material or general dispersal. Can be removed by surgery. Generally not life threatening unless in an inoperable place, e.g. certain types of brain tumour.

• Malignant: tumour can invade surrounding material and generally disperse in the body. Often life threatening.

• Metastasis or secondaries: spreads from the main site of the tumour to a distant site, forming new centres of growth.

• Neoadjuvant therapy: can be used to shrink a large tumour so that it can be more easily removed by surgery.

Major Groups of Cancer

Carcinomas

• Solid tumours usually from epithelial cells.

• 90% of all human cancers.

Usually found in:

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