Frameshift or splice variants in JAK1, DNMT3A, TET2 and TYK2 all occurred in individuals with a history of CM and lymphoma/leukaemia and are not previously described as haematological malignancy hotspots; each of these individuals additionally had prostate and/or colorectal cancer, suggesting a potential phenotype associated with these variants. The gene discussed is JAK1; the disease is cutaneous mastocytosis.