As the molecular pathology of pituitary cell development and the process of tumorigenesis in this organ continues to advance, it is recommended that pituitary neuroendocrine tumors(PitNETs)be classified based on three lineage-specific transcription factors(PIT1, Tpit, and SF1). In the hyperaging society of Japan, the number of cases traditionally classified as nonfunctioning PitNETs is increasing, and it is possible that some of these tumors may be associated with tumors that are known to exhibit aggressive behavior. The molecular pathological background of PitNET development is highly variable, and its pathogenesis in many cases remains unclear. As genomic analysis of PitNETs progresses, it is becoming increasingly clear that abnormalities in germline and somatic cell genomes contribute to our understanding of their etiology but do not explain most of them. Epigenetic modifications, such as deoxyribonucleic acid methylation and histone modifications(methylation and acetylation), are thought to be intricately related to tumorigenesis.