Risk and adverse clinical outcomes of thrombocytopenia among patients with solid tumors-a Danish population-based cohort study

Background: Knowledge about thrombocytopenia among patients with solid tumors is scarce. We examined the risk of thrombocytopenia among patients with solid tumors and its association with adverse outcomes. Methods: Using Danish health registries, we identified all patients with incident solid tumors from 2015-2018 (n = 52,380) and a platelet count measurement within 2 weeks prior to or on their cancer diagnosis date. The risk of thrombocytopenia was categorized as grades 0 (any platelet count x 10(9)/L): <150; 1: <100; 2: <75; 3: <50; 4: <25, and 5: <10. To study the outcomes, each patient with thrombocytopenia was matched with up to five cancer patients without thrombocytopenia by age, sex, cancer type, and stage. Cox regression was used to compute hazard ratios (HRs) of bleeding, transfusion, or death, adjusting for confounding factors. Results: The 1-year risk of thrombocytopenia was 23%, increasing to 30% at 4 years. This risk was higher in patients receiving chemotherapy (43% at 1 year and 49% at 4 years). Overall, patients with thrombocytopenia had higher 30-days rates of bleeding (HR = 1.72 [95% confidence interval, CI: 1.41-2.11]). Thrombocytopenia was also associated with an increased rate of transfusion, and death, but some of the risk estimates were imprecise. Conclusions: The risk of thrombocytopenia was substantial among patients with solid tumors and associated with adverse outcomes.