The Diagnostic Evolution of Haematological Neoplasms: A Narrative Review of the Road to Two Genetically Focused Classification Systems Through a Resource-Limited Perspective

<b>Introduction:</b> Classification of haematological malignancies has evolved over centuries from multiple morphology-based classifications to a single consensus classification, the World Health Organisation (WHO) classification of tumours in 2001, which included clinical history and immunophenotype. The next two decades saw a revised WHO classification, incorporating immunophenotyping, cytogenetics, molecular genetics, morphology, and clinical features. In 2022, the WHO classification of Haematolymphoid Tumours fifth edition (WHO-HAEM5) and International Consensus Classification (ICC) integrated advanced genetic technologies. Navigating two classifications has caused uncertainty for pathologists and clinicians globally. However, there is added concern for low and middle income countries (LMICs), where diagnostic disparities compared to high income countries (HICs) already exist. The incorporation of advanced and costly genetic testing will likely widen this gap. This disparity and diagnostic evolution are the focus of this review. <b>Methods:</b> A literature search was performed for articles reporting on historical evolution of haematological malignancy diagnosis, diagnostic challenges for haematology in LMICs, haematological classification systems, overall survival, and laboratory turn-around times was performed using three scholarly databases; and a Google search was made for historic portions of this review. Ninety-two publications were included. <b>Results:</b> This narrative review describes the diagnostic and genetic evolution of haematological malignancies, and highlights disparities of laboratory diagnostics between LMICs and HICs. <b>Conclusions:</b> The existing disparities in diagnostic haematology between LMICs and HICs will likely widen due to the emphasis on advanced genetic testing in the WHO-HAEM5 and ICC. Advocacy for consistent accessibility and affordability of haematology diagnostics in LMICs is needed.