A paper appeared in Nature Communications, an online, open-access and peer-reviewed scientific journal, on October 8 2019. The authors described a new test on blood serum that could help general practitioners to identify those patients requiring imaging of the brain (CT or MRI scanning) for suspected brain tumours. A specific biochemical footprint, derived from the spectral output obtained by exposing a sample of blood to infrared light, was used to help identify brain cancer. The test was initially performed on 724 stored blood samples, previously obtained from patients with brain cancers and controls free from brain cancer. The test results were used to train a support vector machine algorithm-a form of artificial intelligence. The test was then validated prospectively on 104 patients referred for brain imaging for, or newly diagnosed with, brain tumours. The early results are promising. There is some way to go, however, before any such test is used more widely. The need for this type of testing arises because the diagnosis of brain cancer can be difficult and is frequently missed.
Brain cancers are rare forms of cancer. According to Cancer Research UK, 11,725 people were diagnosed in the UK with brain tumours during 2014-16, while they accounted for 5,250 deaths in 2015-17. The average GP is expected to see around three or four patients with new brain tumours during an entire working career. The large majority of people seen with headache in primary care have other underlying diagnoses.
Unfamiliarity with brain cancer, added to the frequently non-specific nature of early symptoms, means that diagnosis is frequently delayed. Many patients make frequent visits to their GP, and are finally diagnosed in an emergency department when their condition suddenly deteriorates or when they go seeking a second opinion. Brain tumours are the commonest type of cancer to be diagnosed as an emergency presentation in the UK, frequently presenting with fits or loss of consciousness, or mimicking strokes. Over 60 per cent of patients with primary brain tumours are thus first diagnosed by emergency doctors. While only around two per cent of emergency department attendances are because of headache, the likelihood of identifying serious causes of headache is much higher in this group of patients.
Early symptoms of brain tumours include headache, altered behaviour and personality, memory changes, and visual problems. These symptoms overlap with a variety of other conditions, most of which are neither life-threatening nor life-changing. Most brain tumours grow silently and slowly for long periods of time before neurological features develop, often when pressure within the skull starts to rise abruptly and precipitously. Part of the problem is that the brain itself is insensitive to pain. For headache to develop, it requires some form of involvement of pain-sensitive structures within the skull, such as the lining meninges or the arteries and veins.
Headache is a particularly important early symptom of brain tumours. Doctors are taught the importance of recognising red flags in the history of headache which may signify an increased risk of a brain tumour. These include progressive and severe headache of recent onset, early-morning headache, headache that awakens one from sleep at night, headache associated with vomiting, headache worsened on coughing, and headache associated with changes in mental state. Recognition of one or several red flags in the patient’s history lowers the doctor’s threshold for requesting a brain scan.
Ideally, a patient with an early brain tumour should be recognised at the first visit by his or her GP and referred for urgent imaging of the brain, with either a contrast-enhanced (facilitated with a radiopaque dye) CT scan or an MRI scan. This is unlikely to happen in the near future. Headache is a common symptom while brain tumours are rare. Scans may be difficult to obtain in a timely fashion, are expensive, and may involve unnecessary exposure to ionising radiation (in the case of CT scans). The ability to screen people suspected of harbouring brain tumours using a readily available blood test , when one does eventually become available, holds promise for the future and will allow earlier diagnosis of brain cancer and better outcomes for patients.
Ashis Banerjee (worked in both neurosurgery and in emergency medicine)