PB0753 - Platelet count as a novel diagnostic marker for early lung cancer diagnosis: an epidemiological study

Background: Two-thirds of lung cancer patients are diagnosed at an advanced stage, often following the onset of symptoms such as haemoptysis. Thrombocytosis is a positive predictive marker for lung cancer and is often present before other symptoms.

Aims: To determine when the platelet count begins to rise before a lung cancer diagnosis, and to ascertain whether thrombocytosis is equally indicative of its three main histological subtypes: adenocarcinoma (ADC), squamous cell carcinoma (SCC), and small cell lung cancer (SCLC).

Methods: We designed a matched cohort study to analyse primary care records from the Clinical Practice Research Datalink (CPRD) with linkage to the cancer registry. There were 4,720 lung cancer patients (2,355 ADC, 1,546 SCC, and 819 SCLC) matched on age, sex, and practice at a ratio of 1:5 to 23,076 healthy controls. Fractional polynomial regression predicted the rise in platelet count in the days preceding lung cancer diagnosis, and the z-test for independent proportions compared pre-diagnostic thrombocytosis occurrence across subtypes.

Results: The platelet count began to rise 300 days before lung cancer diagnosis, with SCC patients experiencing a significantly faster rise than ADC and SCLC patients. At diagnosis, 22.6% of SCC patients had thrombocytosis (95% CI: 20.5%-24.7%) which was significantly higher than 15.5% of ADC (95% CI: 14.1%-17.0%, p< 0.0001) and 16.1% of SCLC patients (95% CI: 13.6%-18.6%, p< 0.001).

Conclusion(s): Thrombocytosis is more common in SCC than other subtypes. The steady rise in platelet count leading up to a lung cancer diagnosis may indicate that GPs should consider lung cancer in patients with an otherwise unexplained increase in platelet numbers, even below the thrombocytosis threshold. As stimulation of thrombopoiesis occurs at least 300 days before a lung cancer diagnosis, these unknown stimulatory factors could serve as novel biomarkers to significantly expedite lung cancer diagnosis.