The relationship between IL-6 and thrombocytosis accompanying gastrointestinal tumours

Introduction
Several reports have stated that thrombocytosis is associated with worse survival and higher rate of metastasis in solid tumours. A study in ovarian tumours implicated IL-6 produced by tumour cells as a key mechanistic factor.

Aim
To evaluate the relevance of this paraneoplastic pathway in gastrointestinal cancer.

Material and methods
After excluding thromboembolic and inflammatory disorders, 161 patients were enrolled who had been operated due to various gastrointestinal cancer at the 1st Department of Surgery at the Semmelweis University between 2015 and 2017. Platelet counts and serum IL-6 levels were determined from preoperative blood samples. Thrombocytosis was defined as the upper limit of normal platelet count, e.g. 400 × 103/μl.

Results
A weak but significantly positive correlation was found between elevated platelet counts and serum IL-6 (correlation coefficient: R = 0.214, p = 0.006), which became more pronounced in colon and oesophageal cancer if evaluated in the different tumour types (R = 0.292 and R = 0.419, respectively). However, using a multivariant linear regression model (R2 = 0.47) corrected with haemoglobin, white blood cell count, and advanced disease stage, the analysis showed no significant correlation between serum IL-6 and platelet counts.

Conclusions
In gastrointestinal cancer our study did not support the paracrine-mediated paraneoplastic pathway described in ovarian tumors. Thrombocytosis showed significant correlation with white blood cells instead of serum IL-6, which implies that the inflammatory process may influence both parameters. Further studies are needed on larger patient cohorts.