Chemotherapy

What is chemotherapy and how it works?

Chemotherapy is a mainstay in cancer treatment using chemical substances (medications). To the contrary, of surgery and radiation therapy that treat a localized disease, chemotherapy is used to treat a systemic disease.
 

To understand the mechanism of chemotherapy action it is essential to understand the cell cycle. Normal cells undergo division and replication in a regulated manner. Normal cells remain in adhesion with cells in contact in a tightly controlled manner.
Cancer cells on the other hand escape this control mechanism and continue to divide with no stop. Cancer cells lose cell-to-cell contact regulations and evolve new potentials that allow them to spread and grow in different parts of the body.
 

Cell function and fate can be directed by the control of gene expression (DNA/RNA level) as well as posttranscriptional regulation. Chemotherapy acts mainly on replicating cells during the cell cycle by interfering at different levels from DNA synthesis to protein function. They can work at any point of the cell cycle (cell-cycle specific- phase non-specific) but some works only in specific phase of the cycle (phase specific). Other chemotherapeutics act on cells whether they are in the cell cycle or resting and are named cell-cycle nonspecific drugs.
 

Routes of administration:
 

Chemotherapy drugs are given mainly by intravenous route.
 

Other routes include the following:
- Intramuscular
- Oral (by mouth)
- Subcutaneous
- Local into a cavity (intrapleural, intraperitoneal, intrathecal) or
- Topical directly to the skin.

- Intra-arterial.
 

Cell cycle specific are most effective when given at interrupted doses or long infusion (12-24 hours) while cycle non-specific are most effective when given at bolus doses (short infusion once).

Regimens:

Chemotherapeutic drugs are usually given in a combination form of two drugs or more what is known as chemotherapy regimen. This is to achieve maximum efficacy, overcome possible evolving resistance and the possible heterogenousity of the tumor (more than one cell of origin with different biological behavior). Drug combination and doses are tested at different levels of clinical trials to ensure the maximum safety and efficacy.
Since chemotherapy is a systemic treatment that circulates in th blood, it can affect the different cells of the body in addition to tumor cells. The regimen is given in the form of cycles with specific periods of intervals (rest from days to weeks) to allow the recovery of the different body systems from its effect.
 

Treatment Strategies:
 

- Adjuvant treatment:
Chemotherapy that is given according to certain risk factors after the complete excision of tumor is known as an adjuvant treatment. It aims to prevent the recurrence of the disease.
 

- Neoadjuvant Chemotherapy:
Chemotherapy that is given prior to surgery is named neoadjuvant treatment. It aims at decreasing (down-staging) the tumor to allow safe and proper complete surgical excision.
 

- Multimodality treatment:
When different modalities of treatment are used to treat cancer, it is named multimodality treatment approach like chemotherapy with radiotherapy and/or surgery.