Alternative RNA Splicing in Cancer: Molecular Mechanisms, Functional Consequences, Biomarkers and Therapeutic Opportunities.

Alternative pre-mRNA splicing is a central layer of gene regulation that enables a limited number of genes to generate a far larger and more context-dependent transcriptome and proteome. In cancer, splicing is disrupted by mutations in cis-regulatory sequences, recurrent lesions in spliceosome components, altered abundance or activity of RNA-binding proteins, and changes in transcription, chromatin, RNA modification, metabolism and stress signalling. These alterations are not merely by-products of malignant transformation. They can create oncogenic protein isoforms, eliminate tumour-suppressive products, remodel cellular identity, promote metastasis and drug resistance, and generate tumour-restricted peptides that are visible to the immune system. Large pan-cancer datasets, long-read sequencing, single-cell isoform profiling, proteogenomics and functional perturbation screens are now resolving this complexity at unprecedented scale. In parallel, multiple therapeutic strategies are advancing, including modulators of the SF3B complex, molecular glues that degrade RBM39, inhibitors of protein arginine methyltransferases and splicing kinases, splice-switching oligonucleotides, programmable RNA-targeting systems, and vaccines or T-cell receptors directed against splicing-derived neoantigens. This review integrates the molecular logic of splice-site selection with the cancer-specific mechanisms that perturb it, summarizes representative isoform switches across the hallmarks of cancer, evaluates emerging technologies and clinical biomarkers, and discusses the opportunities and constraints of translating splicing biology into precision oncology. Particular emphasis is placed on tumour specificity, intratumoural heterogeneity, proteomic validation, therapeutic windows and rational combination strategies.