Appreciate that society needs to assess the balance between the benefits…

The idea

Cisplatin is among the most effective anticancer drugs ever made; testicular cancer, once usually fatal, is now cured in the great majority of cases largely because of it. The harm comes from the same chemistry: platinum binds to guanine in whatever cell it reaches, not only in a tumour, so healthy tissues whose cells divide quickly suffer most. That is why patients lose hair, feel sick and become vulnerable to infection as the bone marrow makes fewer white cells, and why kidney damage and hearing loss are monitored. Weighing those costs against years of life gained is not a judgement chemistry can make alone; it involves the patient's informed consent, clinicians, regulators and the cost to a health service. Research into targeted delivery aims to cut the dose reaching healthy tissue.

What earns the marks

• Stating that the drug also affects healthy cells and not only cancer cells.
• Naming a rapidly dividing healthy tissue such as bone marrow, hair follicles or the lining of the gut.
• Naming a specific adverse effect and linking it to the tissue affected.
• A balanced judgement that names a benefit as well as a risk.

Common mistakes and how to put them right

• Answering only that the drug has side effects, without saying why healthy cells are attacked.

• Claiming the drug can tell a cancer cell from a healthy one.

• Listing adverse effects with no benefit at all when the question asks for a balance.

• Writing about cost or ethics in general terms without any chemistry of the drug.

Exam tips

• A question that says discuss or evaluate wants both sides, so write at least one benefit and one adverse effect explicitly.
• Tie each adverse effect to a tissue whose cells divide quickly, which is the chemistry-based reason being looked for.
• Keep the answer specific to this drug; general remarks that all medicines carry risks earn nothing.