Platelet Count and Survival after Cancer

SIMPLE SUMMARY: Platelets are cellular fragments circulating in the blood that are responsible for clotting. Previous research has shown that cancer patients with an abnormally high platelet count (thrombocytosis) have elevated rates of death from cancer. We aimed to investigate to what extent platelet counts are associated with survival after cancer. We followed a large provincial cohort of cancer patients with a platelet count recorded at the time of their diagnosis. We categorized patients according to platelet count (low, medium, high). Cancer patients in the ‘high’ platelet count category had the highest rate of cancer death, and cancer patients in the ‘low’ platelet count category had the lowest rate of cancer death. Platelet count may be used to predict survival in cancer patients. ABSTRACT: Thrombocytosis is associated with cancer progression and death for many cancer types. It is unclear if platelet count is also associated with cancer survival. We conducted a cohort study of 112,231 adults in Ontario with a diagnosis of cancer between January 2007 and December 2016. We included patients who had a complete blood count (CBC) completed in the 30 days prior to their cancer diagnosis. Subjects were assigned to one of three categories according to platelet count: low (≤25th percentile), medium (>25 to <75th percentile), and high (≥75th percentile). Study subjects were followed from the date of their cancer diagnosis for cancer-specific death. Of the 112,231 eligible cancer patients in the cohort study, 40,329 (35.9%) died from their cancer in the follow-up period. Relative to those with a medium platelet count, the rate of cancer-specific death was higher among individuals with a high platelet count (HR 1.52; 95%CI 1.48–1.55) and was lower among individuals with a low platelet count (HR 0.91; 95%CI 0.88–0.93). A high platelet count was associated with poor survival for many cancer types. Platelet count could potentially be used as a risk stratification measure for cancer patients.