T-cell receptor (TCR) clonality assessment is a principal diagnostic test in the management of mycosis fungoides (MF). However, current polymerase chain reaction–based methods may produce ambiguous results, often because of low abundance of clonal T lymphocytes, resulting in weak clonal peaks that cannot be size-resolved by contemporary capillary electrophoresis (CE).

We sought to determine if next-generation sequencing (NGS)-based detection has increased sensitivity for T-cell clonality over CE-based detection in MF.

Clonality was determined by an NGS-based method in which the TCR-γ variable region was polymerase chain reaction amplified and the products sequenced to establish the identity of rearranged variable and joining regions.

Of the 35 MF cases tested, 29 (85%) showed a clonal T-cell rearrangement by NGS, compared with 15 (44%) by standard CE detection. Three patients with MF had follow-up testing that showed identical, clonal TCR sequences in subsequent skin biopsy specimens.

Clonal T-cell populations have been described in benign conditions; evidence of clonality alone, by any method, is not sufficient for diagnosis.

TCR clonality assessment by NGS has superior sensitivity compared with CE-based detection. Further, NGS enables tracking of specific clones across multiple time points for more accurate identification of recurrent MF.