The right treatment for the right patient at the right time

The last 20 years has seen huge advances in our understanding of how cancer arises and how it may be effectively treated. This has led to the development of drugs which are targeted at vulnerabilities within cancer cells which are not found in normal tissues. These precision medicines can be highly effective- but only if given to the right patient at the right time.

what is precision medicine?

A cancer starts when a cell either starts dividing when it shouldn’t or doesn’t die when it should. By carefully examining cancer cells in the laboratory, it is now possible to define exactly what causes this to happen in many cases. This in turn has led to the development of drugs which can stop cancer cells dividing or stimulate them to die, whilst leaving normal cells relatively unaffected.

This is a major advance over older forms of treatment such as chemotherapy. Chemotherapy drugs typically work by reducing cell division in all rapidly dividing cells- not just those which have formed a cancer. This often leads to significant side effects on cells such as those lining the gut and mouth and those in the bone marrow which form components of the blood.

The first effective example of these newer precision medicines was developed to treat a type of blood cancer called chronic myeloid leukaemia (CML). This disease is almost always associated with a specific abnormality in the chromosomes of blood forming cells. Chromosomes are structures found in the cell nucleus which contain the cell’s DNA. DNA controls the way in which cells divide. Every cell in the body, apart from sperm and eggs, contain 23 pairs of chromosomes- numbered in order of size from 1, the largest, to 23, the smallest. In CML breaks form in chromosomes 9 and 22 and they glue together to form abnormal chromosomes. This leads to the cell producing a protein never seen in normal cells which instructs the cell to divide when it shouldn’t. This so called bcr-abl protein is a perfect drug target and in 2001 the treatment of CML was revolutionised by the introduction of a drug now known as imatinib- turning it from a life-shortening to a chronic disease in most cases.

The success of imatinib led the way to intense efforts to identify similar abnormalities in other tumour types. Although few other cancers have been found which have such a clear-cut vulnerability to aim for there are many good examples where precision medicines can delay or halt tumour development- with relatively few side effects. However, precision medicines only work if they are accompanied by an accurate diagnosis. This usually involves specialised tests to demonstrate that the drug target is present in an individual case. For example, the drug Herceptin will only work if breast cancer cells have the drug target- HER2. The drug is ineffective if this isn’t the case.

The targeting of drugs to very specific targets presents a challenge to the introduction of new treatments as patients can only be included in a clinical trial if they have a tumour with the appropriate form of cancer. Finding enough volunteers to take part in a study often causes significant delays in bringing active drugs to the clinic. RareCan aims to reduce these delays by collecting the relevant information about patients who are interested in taking part in research so that these studies can be undertaken more quickly.

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