Diagnostic and prognostic classification of atypical spitzoid tumours based on histology and genomic aberrations: A prospective cohort study with long-term follow-up

•Atypical spitzoid tumours (ASTs) exhibit a continuum of chromosomal aberrations.•Histology of ASTs does not reliably reflect the extent of chromosomal aberrations.•ASTs with and without chromosomal aberrations have an excellent prognosis.•Sentinel lymph node status has no prognostic relevance in ASTs.•ASTs with complex chromosomal aberrations should undergo clinical follow-up.