Early detection

Early detection covers screening of healthy people, faster diagnosis of people with symptoms, and surveillance of those at high risk (BRCA carriers, Lynch syndrome, cirrhosis, Barrett's oesophagus); it works because many cancers spend years growing locally before they spread. Its limits are cancers that spread early or grow from tissue that is hard to image (pancreas, ovary, some lung cancers), and the overdiagnosis of slow cancers that would never have mattered. New approaches include blood tests for tumour DNA and proteins, AI reading of routine scans, and risk-based rather than age-based screening; whether they reduce deaths rather than just shift the stage at diagnosis is the key question.