# Real-World Impact of Deep Targeted Sequencing on Erythrocytosis and Thrombocytosis Diagnosis: A Reference Centre Experience

## TL;DR

This study evaluates how deep targeted sequencing impacts the diagnosis of erythrocytosis and thrombocytosis in a real-world setting, finding limited benefit and suggesting better patient selection could improve outcomes.

## Contribution

The paper provides real-world evidence on the diagnostic yield of NGS in unexplained erythrocytosis and thrombocytosis, emphasizing the need for improved patient selection.

## Key findings

- Only 11.9% of erythrocytosis patients and 25.9% of thrombocytosis patients had actionable variants detected via NGS.
- NGS identified familial or clonal disorders in a subset of patients previously classified as idiopathic.
- The study highlights the importance of pre-NGS screening to improve diagnostic yield.

## Abstract

Around 70% of cases of erythrocytosis are categorised as “idiopathic” after excluding secondary causes and polycythaemia vera. A similar situation arises in the setting of thrombocytosis, with even a 15% of essential thrombocythemia lacking canonical mutations. Previous studies have shown that a deeper investigation of these patients can unmask underlying primary conditions (such as familial disorders or a clonal disease without canonical mutations). The role of next-generation sequencing (NGS) in their diagnosis has been explored in a retrospective manner, showing promising results. In this study, we reviewed the impact of NGS performed in our centre on the diagnosis of erythrocytosis and thrombocytosis (117 and 58 patients, respectively). Our findings showed that few patients benefited from this test, since only 11.9% and 25.9% showed a variant leading to diagnosis of a primary disorder, respectively. However, we believe that this yield could be improved through a better selection prior to NGS.

Despite advances in diagnosis of erythrocytosis and thrombocytosis due to driver mutation testing, many cases remain classified as “idiopathic”. This can be explained by the absence of an evident secondary cause, inconclusive bone marrow biopsy or neglection of family history. Analysis of a broad panel of genes through next-generation sequencing (NGS) could improve diagnostic work-up identifying underlying genetic causes. We reviewed the results of NGS performed in our laboratory and its diagnostic impact on 117 patients with unexplained erythrocytosis and 58 with unexplained thrombocytosis; six patients (5.1%) were diagnosed with polycythaemia vera (PV) and 8 (6.8%) with familial erythrocytosis after NGS testing. Low EPO and a family history seemed to predict a positive result, respectively. However, a greater percentage of patients were ultimately diagnosed with secondary erythrocytosis (36%), remained as idiopathic (28.2%) or were self-limited (15%). The yield of NGS was shown to be slightly higher in patients with thrombocytosis, as 15 (25.9%) were diagnosed with essential thrombocythemia (ET) or familial thrombocytosis after variant detection; previous research has shown similar results, but most of them carried out NGS retrospectively, while the present study exhibits the performance of this test in a real-world setting. Overall, the low rate of variant detection and its poor impact on diagnostic work-up highlights the need for a thorough screening prior to NGS, in order to improve its yield.