2. Resistance

Tumours can become resistant to some targeted anti-cancer medicines. This means that a tumour is treated by a medicine at first with success, but the medicine stops working later on. It is thought that further mutations in tumours can cause resistance and tumours tend to mutate frequently.

Resistance is also an issue with viral and bacterial infections, such as HIV or Tuberculosis, when the amount of medicine in the blood stream/tissues is not regular.

With the medicine ‘vemurafenib’, which is used to treat melanoma, three forms of resistance have been found so far. For example, new mutations can activate ‘new’ signalling pathways in the tumour to cause cell growth. This can ‘bypass’ the pathway that the medicine is blocking, so that the medicine can no longer stop cell growth.

Treatment with more than one medicine may be one way to avoid resistance.