Elevated platelets may signal increased cancer risk

Platelets (thrombocytes) are active for more than just adhesion and cohesion in the formation of a 'hemostatic plug' (blood clot), along with activation of coagulation mechanisms. Platelets also have important secretory functions that release growth factors and communicate with white blood cells and cells that line blood vessels (endothelial cells). Through this they promote inflammation and tissue proliferation (as in wound healing). Now an important study published in the British Journal of General Practice that an increase in platelet count is clinical risk marker for cancer. The authors note:

"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. One feature of possible cancer has only recently been recognised to have diagnostic potential: a raised platelet count, or thrombocytosis."

Platelets as predictors

Earlier studies have shown the predictive value of thrombocytosis for certain cancers, but none have looked at cancer in general.

"Revised UK national guidance for suspected cancer incorporates thrombocytosis in some of its recommendations for lung, oesophagogastric, and uterine cancers. However, no study has examined thrombocytosis in primary care for all cancers. This study aimed to address that gap."

The authors examined 1-year data for two groups of subjects: 40,000 patients aged ≥40 years with a platelet count of more than 400 × 10⁹/L (10⁹/L = 10³/uL) and 10,000 matched patients with a normal platelet count. Clinicians, note the reference range: >400 x 10³/uL = thrombocytosis. Their data did show that elevated platelets should be regarded as a cancer risk factor, especially for lung and colorectal cancer."A total of 1098 out of 9435 males with thrombocytosis were diagnosed with cancer (11.6%), compared with 106 of 2599 males without thrombocytosis (4.1%). A total of 1355 out of 21 826 females with thrombocytosis developed cancer (6.2%). The risk of cancer increased to 18.1% for males and 10.1% for females, when a second raised platelet count was recorded within 6 months. Lung and colorectal cancer were more commonly diagnosed with thrombocytosis."Very importantly:

"One-third of patients with thrombocytosis and lung or colorectal cancer had no other symptoms indicative of malignancy."

The authors summarize their findings:

"This large-scale cohort study is the first from primary care to report the overall risk of cancer in patients with thrombocytosis, compared with those with normal platelet counts. Males with thrombocytosis had an 11.6% incidence of cancer in the following year, and females had an incidence of 6.2%: this compares with 4.1% of males with normal platelet counts. The incidence of cancer rose with age and with a higher platelet count, and at least one-third of patients with lung and colorectal cancer with pre-diagnosis thrombocytosis had no other symptoms indicative of malignancy."

Commenting in Medscape Family Medicine...

"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."