Abnormalities involving class I HLA are frequent in many lymphoma subtypes but have not yet been extensively studied in cutaneous T-cell lymphomas (CTCL). We characterized the occurrence of class I HLA abnormalities in 65 patients with advanced mycosis fungoides (MF) or Sézary syndrome (SS). Targeted DNA sequencing including coverage of HLA loci revealed at least one HLA abnormality in 26/65 patients (40%). Twelve unique somatic HLA mutations were identified across nine patients, and loss …