To understand why we haven’t cured cancer yet, the most important thing to know is that cancer is not one disease. Instead, it’s an umbrella term for more than 200 distinct diseases.
Each broad cancer type has many sub-types, and they all look and behave differently because they are different on a genetic and molecular level. This is because cancer arises from our own cells, so each cancer can be as different and diverse as people are.
Underlying the more than 200 different cancers are a myriad of different genetic mutations. Every cancer is caused by a different set of mutations and as the tumour grows, more and more mutations accumulate. This means that every tumour has an individual set of mutations, so a drug that works for one cancer patient, might have absolutely no effect on another.
Cancer cells within a single tumour are not identical
Not every cancer cell in a tumour will have the same genetic mutations as a neighbouring cancer cell. That means that treatments can often kill one type of cell in a tumour, while others survive the treatment, allowing the tumour to grow again.
Treatments can eventually stop working
The genetic mutations that cancer cells acquire over time mean that the cells change the way they behave. This can be an incredibly difficult problem during treatment because the mutations can lead to cancer cells developing resistance to a treatment over time, making it ineffective.
If that happens, the patient will then have to be put on to a different treatment – but again, the cancer could develop resistance to the new drug.
Cancer cells are really good at staying alive
Normal cells have certain mechanisms in place that stop them from growing or dividing too much. Cancer cells have lost these control mechanisms and can develop an arsenal of tricks to avoid being killed.