Edit: sorry was trying to quote this:
@Whyhaveibeencutoutofmamsnot
"The news items never explain properly about enhertu.
It is available on the NHS for those with Her2+ breast cancer where it is shown to be more cost effective than in those patients with low Her2+ breast cancer where it is not allowed yet. Perhaps when more results are available....."
This is helpful.
So I think essentially what we have here is that there are different types of breast cancer.
Some cancers have Human Epidermal Growth Factor Receptor 2 (HER2 positive). That means that the protein may be made in excessive quantities. That means the cells divide quicker than usual, and makes it more likely to spread.
HER2 status is established by means of s chemical assay (test) and essentially previously it was qualitative (i.e. yes - positive, or no - negative) but now that test is quantitative so, recognising that people can have different levels of HER2 proteins.
The drugs in question are monoclonal antibodies (i.e. a single antibody where every antibody in the drug is identical), attached to chemotherapy drugs. The monoclonal antibodies are like locks which only fit a HER2 shaped key.
So if a cancer is HER2+ there are lots and lots of keys, so lots of the antibodies will bind to the right cells, meaning the chemotherapy will target the cancer cells.
But the less HER2 there is, the less effectively it will be targeting those cells.
So that's why it's been approved for HER2+ cancer's, but not HER2 negative or HER2 low cancers. I can see why that's upsetting but it does make sense when you go through it.
I think overall the main advances we should see over the coming years is massively improved sequencing and hopefully a much wider range of monoclonal antibodies so they can bind to more and more cancer types. Because it would be much more effective to have a monoclonal antibody that is against an antigen (protein on the outside of a cell that an antibody can recognise) that a person's cancer has lots of than trying to use monoclonal antibodies against antigens a person has very few of.