MYD88 and primary central nervous system lymphoma: Watanabe and colleagues used a ddPCR approach to demonstrate MYD88 L265P mutations were detectable in CSF from 20/26 cases of CNS lymphoma[69] suggesting that the CSF provides a more reliable source of ctDNA to track PCNSL tumour‐specific mutations than plasma but one must bear in mind that lumbar punctures are certainly more invasive than a routine blood draw.