Its role as a tumour suppressor in leukaemogenesis has recently gained prominence in that PAX5 inactivation has been shown to be one of the most common genetic alterations in pre‐B ALL and results in a reversible differentiation block (Mullighan et al, 2007, 2008, 2009; Nebral et al, 2009; Liu et al, 2014). The gene discussed is PAX5; the disease is neoplasm.