Blood markers for cancer

### What you need to know A 61 year old man with a one month history of back pain visits his general practitioner (GP). He has hypertension, has never smoked, and reports fatigue for several months. The pain is keeping him awake at night. He has not lost weight. Clinical examination is normal. The differential diagnosis for this patient is wide, including potential malignant causes such as pancreatic, myeloma, and prostate cancer or metastatic disease. Cancer can be difficult to identify, as many of the common symptoms are non-specific and low risk, and even the most well known “alarm” symptoms have relatively low positive predictive values (PPVs) for underlying malignancy.1 For example, weight loss has a PPV for underlying malignancy of only 0-3.3%,2 while rectal bleeding has a PPV of 2.2-15.8%.3 Cancer markers used in hospital settings, when applied to low risk primary care patients, have low positive predictive values and high false positive rates.4 Identifying patients whose non-specific symptoms may be caused by cancer, rather than benign disease, is therefore a challenge for primary care physicians. While formal diagnosis usually happens in secondary care, the first suspicion of cancer generally occurs in primary care. Patients whose symptoms represent an approximate risk of cancer of ≥3% are recommended by the National Institute for Health and Care Excellence (NICE) for urgent investigation, often by referral.5 Those with estimated risk <3% may receive …