Abstract
BackgroundThrombocytosis (raised platelet count) is an emerging risk marker of cancer, but the association has not been fully explored in a primary care context.AimTo examine the incidence of cancer in a cohort of patients with thrombocytosis, to determine how clinically useful this risk marker could be in predicting an underlying malignancy.Design and settingA prospective cohort study using Clinical Practice Research Datalink data from 2000 to 2013.MethodThe 1-year incidence of cancer was compared between two cohorts: 40 000 patients aged ≥40 years with a platelet count of >400 × 109/L (thrombocytosis) and 10 000 matched patients with a normal platelet count. Sub-analyses examined the risk with change in platelet count, sex, age, and different cancer sites.ResultsA total of 1098 out of 9435 males with thrombocytosis were diagnosed with cancer (11.6%; 95% confidence interval [CI] = 11.0 to 12.3), compared with 106 of 2599 males without thrombocytosis (4.1%; 95% CI = 3.4 to 4.9). A total of 1355 out of 21 826 females with thrombocytosis developed cancer (6.2%; 95% CI = 5.9 to 6.5), compared with 119 of 5370 females without (2.2%; 95% CI = 1.8 to 2.6). The risk of cancer increased to 18.1% (95% CI = 15.9 to 20.5) for males and 10.1% (95% CI = 9.0 to 11.3) for females, when a second raised platelet count was recorded within 6 months. Lung and colorectal cancer were more commonly diagnosed with thrombocytosis. One-third of patients with thrombocytosis and lung or colorectal cancer had no other symptoms indicative of malignancy.ConclusionThrombocytosis is a risk marker of cancer in adults; 11.6% and 6.2% cancer incidence in males and females, respectively, is worthy of further investigation for underlying malignancy. These figures well exceed the National Institute for Health and Care Excellence-mandated risk threshold of 3% risk to warrant referral for suspected cancer.
Highlights
Cancer is one of the leading causes of death in developed countries, with over 163 000 cancer deaths in the UK in 2014.1 The commonest route to cancer diagnosis follows the development of symptoms, and definitive diagnosis by biopsy and access to specialist care often rely on a primary care physician to recognise the possibility of cancer
This represents a 1-year cancer incidence of 11.6% for males and 6.2% for females; this is equivalent to the positive predictive value (PPV) of a raised platelet count
In patients with a normal platelet count there were 106 cancers diagnosed in males and 119 in females; a 1-year cancer incidence of 4.1% in males and 2.2% in females (Table 1)
Summary
Cancer is one of the leading causes of death in developed countries, with over 163 000 cancer deaths in the UK in 2014.1 The commonest route to cancer diagnosis follows the development of symptoms, and definitive diagnosis by biopsy and access to specialist care often rely on a primary care physician to recognise the possibility of cancer. It is generally accepted that delay in symptomatic diagnosis is harmful.[2,3] One feature of possible cancer has only recently been recognised to have diagnostic potential: a raised platelet count, or thrombocytosis. Thrombocytosis (raised platelet count) is an emerging risk marker of cancer, but the association has not been fully explored in a primary care context
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