Tumor microenvironment signature associated with morphology in systemic ALK-positive anaplastic large cell lymphoma

Peripheral T-cell lymphomas (PTCL) are heterogeneous entities whose tumoral microenvironment (TME) may influence disease phenotype and outcome. To dissect their immune and stromal composition, we used two complementary algorithms, CIBERSORTx and MCP-counter, on Affymetrix data from 255 patients whole-tissue biopsies, including 78 systemic anaplastic large cell lymphomas (ALCL). Clustering based on inferred cell proportions revealed a clear separation between ALCL and other PTCL subtypes, including angioimmunoblastic T-cell lymphoma (AITL) and PTCL-not otherwise specified (PTCL-NOS). ALCL-enriched clusters were characterised by granulocytes and macrophages lineages, mast cells, NK cells, memory CD4+ T-cells, as well as fibroblast and endothelial signatures, whereas as expected, AITL cluster was enriched for T-follicular helper cells, B-cells and macrophages. Finally, we focused on 66 ALCL cases with relapse risk and morphological subtype clinical annotations. Distinct TME features enriched in M1 macrophages and monocytes were associated with adverse outcomes and non-common morphological variants. Transcriptomic analyses of mononuclear phagocytes across Affymetrix and RNAseq datasets confirmed distinct clustering according to cell morphology. These analyses identified potential biomarkers associated with uncommon variants and absent from ALK+ ALCL cell lines, confirming their TME origin. Macrophage- and monocyte-related signatures emerged as key contributors in ALK+ ALCL patients heterogeneity, linking TME patterns to tumor morphology and prognosis. These signatures may serve as biomarkers for patient risk stratification and guide the development of targeted therapies.