LGL Clonal Expansion and Unexplained Cytopenia: Two Clues Don't Make an Evidence

Simple Summary The clonal expansions of large granular lymphocytes are frequently detected in a wide spectrum of hematological and immune diseases. This clinical overlap, especially in patients with unexplained cytopenia, makes their diagnostic classification particularly challenging. Herein, we aim to elucidate the boundaries between LGL leukemia (LGLL) and LGL clonal expansions. We also discuss the relevance of LGL clone detection in the diagnostic algorithm, as they might acquire different pathogenetic roles according to the diverse clinical setting. Clonal expansions of large granular lymphocytes (LGL) have been reported in a wide spectrum of conditions, with LGL leukemia (LGLL) being the most extreme. However, the boundaries between LGLL and LGL clones are often subtle, and both conditions can be detected in several clinical scenarios, particularly in patients with cytopenias. The intricate overlap of LGL clonal expansion with other disease entities characterized by unexplained cytopenias makes their classification challenging. Indeed, precisely assigning whether cytopenias might be related to inadequate hematopoiesis (i.e., LGL as a marginal finding) rather than immune-mediated mechanisms (i.e., LGLL) is far from being an easy task. As LGL clones acquire different pathogenetic roles and relevance according to their diverse clinical settings, their detection in the landscape of bone marrow failures and myeloid neoplasms has recently raised growing clinical interest. In this regard, the current availability of different diagnostic techniques, including next generation sequencing, shed light on the relationship between LGL clones and cytopenias, paving the way towards a better disease classification for precision medicine treatments. Herein, we discuss the clinical relevance of LGL clones in the diagnostic algorithm to be followed in patients presenting with cytopenias, offering a foundation for rational management approaches.