Do side effects mean the treatment is working?

No. This is one of the most common beliefs and it is not true. Side effects tell you the treatment is affecting healthy cells too. They do not tell you what is happening to the cancer.

People with almost no side effects are not getting weaker treatment, and people with many are not getting better results. Scans and blood tests are how we tell whether it is working.

Written by two physicians. Checked against patient information from the US National Cancer Institute and Cancer Research UK.