A new finding could improve early detection of cancer among individuals in the general population who are seen by family doctors, say British researchers. They found that patients with increased blood platelet counts (thrombocytosis) are at increased risk for being diagnosed with cancer within a year, particularly if they have a second raised platelet count within 6 months.
The finding comes from a large, population-based study, which was published onlinein the British Journal of General Practice on May 22.
The study showed that 11% of men and 6% of women with thrombocytosis were diagnosed with cancer within the following year.
Crucially, one third of the patients who went on to be diagnosed with lung or colorectal cancer had no other symptoms that would have prompted an urgent referral for cancer.
"It is in this group that thrombocytosis has the greatest potential to prompt earlier diagnosis, where other symptoms have not yet developed. This strongly suggests that cancer should be considered when a result is received showing thrombocytosis, even if cancer was not initially suspected," the researchers comment.
They add that thrombocytosis has not hitherto been widely regarded as a cancer risk factor.
However, their results "show that substantial proportions of lung and colorectal cancer diagnoses could be expedited by at least 2 months if thrombocytosis were to be routinely investigated."
This could yield approximately 5500 earlier diagnoses annually across the United Kingdom.
[P]eople could have their cancer diagnosed up to three months earlier if thrombocytosis prompted investigation for cancer. Dr Sarah Bailey
Lead author, Sarah Bailey, MPH, PhD, research fellow at the University of Exeter Medical School, United Kingdom, said in a statement: "We know that early diagnosis is absolutely key in whether people survive cancer. Our research suggests that substantial numbers of people could have their cancer diagnosed up to three months earlier if thrombocytosis prompted investigation for cancer. This time could make a vital difference in achieving earlier diagnosis."
The researchers conducted a prospective cohort study of data from the UK Clinical Practice Research Datalink, which holds anonymized electronic primary care records from approximately 8% of UK practices.
The team extracted a random sample of 40,000 patients aged at least 40 years who had a platelet count greater than 400 x 109/L recorded between 2000 and 2013 and also identified 10,000 age-, sex- and primary care practice–matched individuals with a normal platelet count.
After exclusions, 31,261 individuals with thrombocytosis were included in the analysis. Their median age was 67.9 years, and 69.8% were female. The final comparison cohort comprised 7969 individuals, with a median age of 68.3 years; 67.4% were female.
Within 1 year of being identified as having thrombocytosis, 11.6% of men and 6.2% of women were diagnosed with cancer. This compared to a 1-year cancer incidence among individuals with a normal platelet count of 4.1% in men and 2.2% in women.
In the second year after identification of thrombocytosis, the incidence of cancer returned to baseline levels.
However, if a second platelet count within 6 months of the first showed an increase or stable platelet count, the 1-year incidence of cancer was 18.1% in men and 10.1% in women.
Staging data were available for 1168 cancers diagnosed in the thrombocytosis group and 123 in the comparison group. This showed that 50.8% of cancer cases in the thrombocytosis group were late-stage disease, compared with 37.4% in the comparison group.
The most commonly diagnosed cancers in the thrombocytosis group were lung and colorectal cancer, at rates higher than those seen in the general population. Conversely, rates of breast and prostate cancer were lower in the thrombocytosis group.
Of patients diagnosed with lung cancer, 35.7% had no symptoms that would warrant urgent investigation in line with the UK National Institute for Health and Care Excellence (NICE) guidelines, aside from thrombocytosis. In colorectal cancer, 32.9% of patients had no other urgent symptoms other than thrombocytosis.
In an interview with Medscape Medical News, lead author Dr Bailey explained that the "main theory" explaining the association between thrombocytosis and cancer risk is that a tumor releases chemicals that increase platelet counts.
While it is tempting to suppose that this could lead to novel treatment targets, Dr Bailey pointed out that there are "so many different factors involved in that process, that I think to target any of those would be a much more complex piece of work."
Another theory is that the rise in platelet counts is "occurring independently of the cancer, but promoting the spread and development of cancer," she said, which "again provides some potential targets for future work."
In terms of future studies, Dr Bailey and colleagues are planning to examine the threshold for increased platelet counts.
She said, "The results that we found were quite significantly above the threshold that NICE guidance currently uses to suggest when patients should become eligible for referral. So we're going to be looking at how raised do platelets have to be to make patients eligible for that referral."
Commenting on the study in an institional press release, coauthor Willie Hamilton, MD, professor of primary care diagnostics of the University of Exeter Medical School, said, "The UK lags well behind other developed countries on early cancer diagnosis…. Our findings on thrombocytosis show a strong association with cancer, particularly in men — far stronger than that of a breast lump for breast cancer in women. It is now crucial that we roll out cancer investigation of thrombocytosis. It could save hundreds of lives each year."
The Policy Research Unit in Cancer Awareness, Screening and Early Diagnosis receives funding for a research programme from the Department of Health Policy Research Programme. Obioha Ukoumunne is supported by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care South West Peninsula. The authors have disclosed no relevant financial relationships.