S297: cancer risk in adult patients with primary immune thrombocytopenia – a danish nationwide cohort study

Background: Survival is reduced among patients with primary immune thrombocytopenia (pITP). The underlying causes most likely involve complications both related to the disease and its treatments. The diagnosis of pITP requires exclusion of alternative causes of thrombocytopenia such as malignant bone marrow disorders that may first become apparent years later. Furthermore, the immune dysregulation present in pITP and the immunosuppressive treatment therapy could increase the risk of cancer. The prognosis of cancer is highly dependent on early detection, and knowledge on cancer risk in patients with pITP may therefore impact clinical follow-up. Previous studies have shown higher risk of some cancers in pITP, as well as higher risk of death from hematological cancer. However, long-term data quantifying incident risk of both solid and hematological cancer in pITP are sparse. Aims: We investigated the risk of incident solid and hematological cancer following a diagnosis of primary ITP compared to the general population. Methods: Newly diagnosed patients with pITP ≥18 years were identified in nationwide Danish health registries during 1980-2016 by using the first registration of the designated ITP diagnosis ICD codes. We excluded patients with prevalent ITP before study period, other thrombocytopenic disorders, and secondary ITP defined as one or more associated diagnosis registered any time before or up to 30 days after diagnosis of ITP. Each patient was age-sex matched with up to 40 general population comparators. Date of the first ITP registration marked start of follow-up, and comparators were assigned the same index date. We identified incident cancers after index date +30days, and divided them in solid and hematological cancer and subgroups of these. Patients and comparators with prevalent hematological cancer at the time of ITP diagnosis were excluded. Analyses were adjusted for comorbidity (prevalent solid cancer, chronic pulmonary disease, diabetes and liver disease). We followed patients with pITP and comparators from index date until the first of cancer, death, emigration, or end of study. We estimated 1-year, 5-year, 10-year and overall cumulative incidence proportions, and 5-year cause-specific hazard (csHR) and subhazard ratios for cancer. Analyses were stratified on age, sex, and time periods. Results: We included 4,768 patients with pITP and 189,662 comparators (56% women, median age 58 years). The 5-year risk was elevated for solid cancer with an adjusted csHR of 1.29 [95% CI 1.14-1.46], and 7.43 [6.08-9.08] for hematological cancer. No differences attributable to sex or age were found. Amongst solid cancer subgroups, the risk of upper gastrointestinal cancer was largest with a csHR of 2.17 [1.49-3.15]. For subgroups of hematological cancer, the risk of leukemia was 9.60 [6.99-13.19] and 4.16 [2.53-6.84] for lymphoma. The 1-year cumulative incidence proportions of solid cancer were 1.92% [1.53-2.38] for patients and 1.19% [1.14-1.25] for comparators, while corresponding numbers for hematological cancer were 0.94% [0.69-1.26] and 0.08% [0.07-0.09] respectively (Figure). However, differences between patients with pITP and comparators diminished over time, and equalized for solid cancer (Figure). Summary/Conclusion: The risk of cancer in patients with primary ITP is elevated, particularly the risk of hematological cancer and in the first years following pITP. Clinical awareness and follow-up should be directed upon this. Details on cancer types, comorbidity and stratified analyses will be presented with the abstract. FigureKeywords: Epidemiology, Immune thrombocytopenia (ITP), Clinical outcome, Cancer