In one study, MYD88 mutations were identified in approximately one‐third of PCNSL cases that harboured the mutation within the tumour sample, with considerably lower variant allelic fractions (VAFs) in the ctDNA compared to tumour DNA[67]; although ctDNA was detectable in about 50–60% of patients in another small series of 14 patients[68]. Here, MYD88 is linked to primary central nervous system lymphoma.