Thrombocytosis: A New Effective Risk Marker for Cancer?

A new study reveals the importance of examining thrombocytosis in primary care for cancer diagnoses.

Cancer is one of the leading cause of death in developed countries. It is critical for primary caregivers to recognize the possibility of cancer and give access to specialists for further diagnosis. Thrombocytosis, an elevated platelet count, is an emerging risk marker of cancer in primary care. Platelets are blood cells in plasma that stop bleeding by forming clots. There are two types of thrombocytosis: primary and secondary thrombocytosis. The cause of primary thrombocytosis is unknown, but secondary thrombocytosis is due to conditions including inflammation, infection, surgery and cancer. In the UK, revised national guidance for suspected cancer includes thrombocytosis in recommendations for lung, oesophagogastric, and uterine cancers. Also, thrombocytosis is an identified marker for types of cancer such as lung, colorectal, renal and uterine. However, not all types of cancer have been studied, and the effect of age, sex, and change in platelet count over time have not been examined.

A new study published in the British Journal of General Practice examined thrombocytosis in primary care and the incidence of all cancers, in an effort to determine the usefulness of thrombocytosis as a clinical risk marker. The researchers used data from the UK Clinical Practice Research Datalink from 2000 to 2013. A total of 50 000 patients who were at least 40 years of age and had a full blood count taken were included in the study. They found that men with thrombocytosis were diagnosed with cancer ~3 times more than men without thrombocytosis (positive predictive value 11.6% vs. 4.1%). Likewise, women with thrombocytosis were ~3 times more likely to develop cancer than women without thrombocytosis (6.2% vs. 2.2%). The most commonly diagnosed cancers with thrombocytosis were lung and colorectal cancer. Breast and prostate cancer were much less commonly diagnosed.

This study did not investigate the mechanism behind thrombocytosis and cancer. The researchers suggest that platelets may potentially assist tumor development by releasing proangiogenic cytokines or supporting metastasis. However, further investigation is required.

To put this into perspective, positive predictive value of a breast lump in a 50-59 years old female for breast cancer is 8.5%. The value of thrombocytosis for cancer was 11.6% in male and 6.2% in female. This suggests that by routinely checking for thrombocytosis in primary care, substantial proportions of lung and colorectal cancer diagnoses could be expedited.




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