This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.
Detecting cancer at the earliest opportunity can improve the chances of successful treatment. New research suggests that a routine blood test could help find cancers early.
Researchers have previously shown that high levels of platelets – cells in the blood that help stop bleeding – can be a sign of cancer. But now they have found that even slightly raised levels of platelets may be an indication of cancer.
This finding could enable family doctors to send their patients for urgent investigation sooner. The results of this University of Exeter study could help improve cancer detection rates in the UK.
What’s the issue?
A normal platelet count is in the range of 150-400 (measured as 150-400 x10⁹ platelets in every litre of blood). Readings above that indicate that something could be wrong.
Platelets stop bleeding by sticking together to form a clot. Too many platelets, a condition called thrombocytosis, may lead to stroke, or heart attack. Research by this team has previously shown that a raised platelet count can also be a warning sign of cancer.
Current NICE guidelines suggest that anyone with a 3% chance of having cancer should be urgently investigated. The group’s previous research suggests that people with thrombocytosis are at much higher risk of cancer than the NICE cut-off, and should be referred for investigation. This has become part of the guidelines.
Now this group has shown that a platelet count in the so-called “high-normal” range of 325-400 is also linked with an increased risk of cancer, and suggest this be included in any updated NICE guidelines.
A figure in this range may be a warning sign, but they stress that a high or high-normal platelet count does not always mean someone is suffering from a serious condition.
But what it can do – and is already doing - is alert GPs that there may be a risk of cancer. Patients can be sent for further investigation at the earliest opportunity.
What’s new?
The study is believed by the authors to be the first of its kind. It included almost 300,000 patients who had blood tests at their GP surgery. Researchers then followed up on how many were diagnosed with cancer within a year. They explored the effects of age, sex and smoking.
They found that:
- cancer incidence increases significantly with age, being male, and higher platelet count
- the risk is greater in men aged 60 and above who have a high-normal count, and rose further for men over 80
- patients with high-normal platelet counts are most at risk of lung, prostate and colorectal cancers and, in general, had advanced-stage cancer at diagnosis
- the chance of being diagnosed with cancer are up to 4.7 times higher for lung cancer and 3.9 times higher for colorectal cancer for patients with high-normal counts
- high-normal platelet count was not found to be a marker of cancer in women in this study; the risk did not meet the UK threshold for urgent investigation.
Why is this important?
The NHS aims to diagnose three out of four cancers at an early stage by 2028, and thus improve treatment outcomes.
Early changes in the body that indicate cancer might lead to diagnosis while the disease is still at the curable stage.
The researchers say that identifying the platelet count which signals an increased risk of cancer could contribute to the improved selection of patients for further investigation. It could also avoid unnecessary investigation in those at lower risk.
The earlier research by the Exeter team is already being used in GP surgeries as a possible warning sign for cancer. The latest findings will be communicated to family doctors and other healthcare professionals involved in detecting and treating cancer, and to policymakers developing guidelines.
What’s next?
The study’s strength lay in the numbers of patients included. But it did not take into account patients’ pre-existing medical conditions, or their current medication.
The research team is applying for funding for further studies to explore this in more detail.
The current study did not detect increased cancer risk among women with high-normal platelet counts, only at levels above 400. Another strand of research will therefore look more closely at the relationship between platelet count and cancer in women.
You may be interested to read
The full paper: Mounce L, and others. Cancer incidence following a high-normal platelet count: cohort study using electronic healthcare records from English primary care. British Journal of General Practice, 2020;70: e622-e628.
A paper by the same researchers had earlier established raised platelet count as a risk marker for cancer. Bailey SER, and others. Clinical relevance of thrombocytosis in primary care: a prospective cohort study of cancer incidence using English electronic medical records and cancer registry data. British Journal of General Practice, 2017;67: e405-e413.
NICE guideline: Suspected cancer: recognition and referral. NG12. London: NICE, 2017
Ankus E and others. Cancer incidence in patients with a high normal platelet count: a cohort study using primary care data. Fam Pract 2018; 35: 671–675.
Funding: This study was funded by the NIHR Policy Research Programme, conducted through the Policy Research Unit in Cancer Awareness, Screening and Early Diagnosis. It was also supported by Cancer Research UK.
Conflicts of Interest: Two of the authors are involved with the CanTest Collaborative, funded by a Cancer Research UK Catalyst Award, as part of an international team of primary care cancer researchers working on early detection and diagnosis of cancer.
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