T-cell clones of uncertain significance. When is the rogue clone dangerous?

T-cell large granular lymphocyte clones that persist over time and that exhibit molecular and immunophenotypic features closely resembling those of T-cell large granular lymphocyte leukemia (T-LGLL) may be detectable in individuals who lack any clinical or laboratory features supporting a diagnosis of a T-cell malignancy. This condition represents a potential precursor state termed T-cell clones of uncertain significance (T-CUS). T-CUS represents the even more benign extreme of the wide spectrum of clonal T-large granular lymphocyte proliferations, emphasizing the need for an appropriate multiparametric diagnostic assessment that avoids misdiagnosis of T-cell neoplasia. This approach should overcome numerical cut-offs as the sole criteria to differentiate the benign condition from the related malignancies. In particular, genomic aberrancies might prospectively identify individuals who are at risk of progression to a full-blown T-cell malignancy. We herein discuss the significance of these T-cell clones in both healthy and disease states, suggesting molecular assays for tracking early steps of disease.