Stratification versus Personalised
Stratification versus Personalised
As we mentioned in the introduction, the term personalised medicine , as currently used, includes both stratification and personalised, and are often used as synonyms. However, the difference between the two is further explained in the following sections.
Stratification
Stratification, in our context, means defining sub-populations (a group or proportion of patients) according to which disease ‘sub-type’ an individual has been diagnosed with.
For example,
some breast cancers are ‘hormone-receptor positive’, some are ‘HER-2 positive’, some are neither.
Breast cancer
can be linked with the hormones ‘oestrogen’ and ‘progesterone’. Most
breast cancers, but not all, have a large number of oestrogen receptors
(molecules in cells that bind
with oestrogen).
- Oestrogen receptors allow the cells to grow when oestrogen is present - these cells are ‘ER positive’.
- Many of these cells also grow in response to progesterone - they are ‘PR positive’.
Breast cancer cells that are ER
and/or PR positive are likely to respond to medicines that block the
action of oestrogen or progesterone. These are called ‘endocrine
therapies’. Around 60 in every
100 breast cancers (60%) respond to these medicines. The
same medicines will only be effective for around 5 or 10 cases in every
100 (5% to 10%) if the tumour is not ER and/or PR positive.
Some
breast cancer cells also make too much of a protein called
‘Her2/neu’. They are known as ‘HER-2 positive’. These cancers tend to be
aggressive. However, the medicine trastuzumab binds to the
Her2/neu protein. This improves overall survival for HER-2 positive patients with advanced breast cancer.
Some breast cancers are neither ER, nor PR nor HER-2 positive. These tumours are called ‘triple negative’,
and as yet no targeted therapies are available. Therefore, more usual types of chemotherapy will be prescribed.
Personalised
Personalised medicine will be based on a detailed profile of the individual. The sub-population that a patient belongs to, will be identified as described in 4.1 above.
However, personalised medicine
takes a range of other information into account, such as the
individual’s lifestyle and environment (for example, UV light exposure,
diet, smoking, stress).
In other words, a doctor giving personalised
medicine will be able to use targeted (stratified) treatments, but will consider more than just which sub-population the patient belongs to. This should help them make the best decisions about treating the patient’s disease.
Much
more detail can be added to an individual’s profile by ‘whole genome sequencing’. This is a way of analysing the whole of a person’s DNA
rather than testing for variations in just one or a few
genes. It is not a standard clinical technique as yet. But many people
predict that this will change. If so, whole genome sequencing
and other related technologies will help drive forward truly personalised medicine. We will see an overview of technologies including genome sequencing in later modules.