Many recent studies have shown the key role of MDSCs in tumour progression and in dampening antitumour immune responses.19,20 A recent study found that MDSCs express BTK, and treatment with ibrutinib reduces MDSC migration and frequency in vivo during experimental breast carcinogenesis.6 In this context, we analysed the frequencies of MDSCs (CD11b+Gr1+) in the spleens and tumours of vehicle- and ibrutinib-treated mice. The gene discussed is BTK; the disease is neoplasm.