As already reported for radiotherapy, chemotherapy also damages both cells cancers and healthy ones and both, within certain limits, can remedy the damage suffered by resorting to repair mechanisms. On the other hand the effectiveness of chemotherapy is based on the fact that cancer cells replicate more intensively and, therefore, are more exposed to damage and repair themselves with greater difficulty.
Since the chemotherapy molecules are transported by the blood, chemotherapy constitutes a “systemic” approach for the treatment of cancer, that is, it concerns the whole organism, unlike radiotherapy, which, on the other hand, is most often targeted on a specific area. Chemotherapy is often associated with other forms of treatment indicated for each tumor: surgery, radiotherapy, molecularly targeted drugs and immunotherapists.
The main chemotherapy approaches are listed below:
- curative chemotherapy: in some forms of cancer in which chemotherapy eliminates all malignant cells it is curative;
- Adjuvant chemotherapy: after surgical removal of the tumor or radiotherapy, it is administered to destroy any residual malignant cells and thus minimize the risk of relapse;
- neoadjuvant chemotherapy: it is aimed at reducing the size of the tumor, before a local approach, of a surgical or radiotherapy type;
- palliative chemotherapy: it is used when the tumor has metastasized or is otherwise untreatable, and is intended to reduce symptoms and improve the quality of life.
There are over 200 different types of cancer and more than 60 categories of chemotherapy molecules. The main distinction is that between cytostatic drugs, which prevent the replication of cells, but do not destroy the malignant ones already present, and cytotoxic drugs, which induce cell death. The doctor decides the most correct approach for each patient based on the characteristics of the tumor and his general health conditions.
Generally, to treat cancer, several drugs are used at the same time, belonging to different classes and having different mechanisms of action. This approach is preferred to using a single drug at high doses because:
- It “attacks” cancer cells on several fronts;
- involves a lower risk that cancer cells become “resistant” to all drugs present in the combination, developing defense and repair mechanisms;
- avoids the intensification of side effects.
Side effects can manifest themselves, for example, in the form of gastrointestinal disorders, immunosuppression, hair loss, since some types of rapidly replicating healthy cells in our body, such as blood cells, those of the mucous membranes that line the mouth, those of the digestive system and hair bulbs can be damaged more than others by chemotherapy. Precisely to achieve greater potency, without increasing the frequency and severity of side effects, traditional chemotherapeutic drugs are associated with molecularly targeted drugs and immunotherapics.
Traditional chemotherapy associations are often referred to with acronyms, which usually derive from the initials of the names of the individual components. For example, the acronym FOLFOX indicates the association of FOLinic acid, 5 Fluoro uracil, OXaliplatin.
The Therapeutic Window
As previously reported, chemotherapy is most effective against rapidly replicating cells. Among them there are not only cancer cells, but also some of the healthy ones, which are damaged giving rise to the side effects listed below. They are generally transient and controllable. Sometimes, they require changing the type of chemotherapy or reducing the dose.
The higher the dose of chemotherapy administered, the higher the number of normal or cancerous cells affected. This means that a high dose is probably more effective, but more likely to cause important side effects. Conversely, a reduced dose of chemotherapy achieves a lower therapeutic effect, but the treatment is better tolerated by the patient. Major side effects are termed “dose-limiting toxicities” as they limit the maximum amount of chemotherapy that can be used. In general, the therapeutic window of a given drug is the dose interval within which a good therapeutic result is obtained, keeping the side effects at acceptable levels. In the case of chemotherapy, this interval is reduced and side effects due to damage to healthy tissues are usually unavoidable. However, in many cases, side effects can be controlled and treated by allowing higher doses of chemotherapy to be administered, without resulting in increased toxicity.