COIL encodes coilin, the defining component of nuclear Cajal bodies (also called coiled bodies), which are subnuclear organelles involved in the modification and assembly of nucleoplasmic small nuclear ribonucleoproteins (snRNPs). Coilin localizes to these nuclear bodies where it facilitates spliceosomal snRNP assembly and U1 and U2 snRNA binding. The protein also associates with nucleoli and the nucleoplasm more broadly, suggesting roles in ribosomal RNA processing and other nuclear RNA-related functions. COIL has been reported in disease contexts including acute lymphoblastic leukemia, anaplastic large cell lymphoma, and other malignancies such as hepatocellular carcinoma and head and neck squamous cell carcinoma, as well as in non-neoplastic conditions including hypothyroidism and infection. However, the mechanistic relationship between COIL dysfunction and disease pathogenesis remains largely undefined in the retrieved literature. The precise contribution of COIL alterations to cancer development or immune dysfunction warrants further investigation, as does its potential utility as a therapeutic target in these disease states.