To gain insight into the underlying molecular mechanisms of the tumour suppression effect observed in βMen1/Bcat-KO mice, we screened the expression of pivotal factors, including DNA replication licensing factor minichromosome maintenance proteins (MCMs), cyclin family proteins and PBK (PDZ binding kinase), in human and mouse menin-null PNETs. The gene discussed is PCNA; the disease is neoplasm.