DRUG RESISTANCE: The Main Factor Making Cancer Treatment Difficult

In stage 4 (metastatic) cancers, the most effective treatment is usually chemotherapy or, in cancers such as prostate and breast cancer, hormonal therapy. Recently, immunotherapy has also joined these treatments. In other words, if cancer has spread beyond its original organ through the blood or lymph and throughout the body, in addition to local treatments such as surgery and radiotherapy, systemic treatments are needed, meaning cancer medicines such as chemotherapy, hormonal therapy and immunotherapy.

Successful results in cancer treatment are being achieved every day. Developing new-generation drugs and surgical innovations has significantly extended patients’ survival. Advances in genetics also enable more effective, patient-specific treatments. Despite all these efforts, the most important problem encountered in some patients is chemotherapy not working or no response to chemotherapy , expressions describing drug resistance. Treatment resistance is not limited to chemotherapy among cancer medicines; it also occurs with hormonal treatments and immunotherapies.

How Do Cancer Cells Develop “Resistance” to Medicines?

Cancer cells can multiply very rapidly. Conventional chemotherapy drugs target rapidly dividing cancer cells. However, cancer cells quickly begin to develop resistance. This is because cancer cells can alter their genetic structure and activate mechanisms that protect them under stress (this is not unique to cancer cells; for example, influenza-causing viruses can also change their structure and develop resistance to drugs and vaccines).

Two Types of Drug Resistance Occur in Cancer:

1. Primary Drug Resistance: It develops under the influence of certain factors before treatment. Genetic and epigenetic factors are thought to play a role.
2. Acquired Drug Resistance: It develops during or after treatment. The cancer cell’s “genetic” structure is unstable, so it rapidly undergoes mutation . A response to the medicine is seen initially, but resistance later develops.

What Factors Cause Drug Resistance in Cancer?

Drug resistance mechanisms in cancer are an intensely researched subject. The figure below shows the factors causing drug resistance.

Examining tumor tissue reveals cancer cells with different structures. In other words, their genetic structures differ considerably. Some genetically different cells surviving after treatment are “responsible for drug resistance.”

- Related topic: Cancer stem cells

In our next article on this subject, you can read about “how cancer resists medicines and the mechanisms involved.”