STAG2是抑癌基因，编码蛋白是cohesin的亚基SA-2，其是cohesin复合物的组分，其是在减数分裂和有丝分裂中DNA复制后着丝粒处的姐妹染色单体的凝聚所必需的。STAG2的失活突变导致癌症的非整倍体和染色体不稳定性。在黑色素瘤、尤文肉瘤、胶质母细胞瘤、头颈部癌、膀胱癌和髓样肿瘤中发现STAG2的无义突变和缺失，而在胃、结直肠癌和前列腺癌中仅观察到缺失。在髓系恶性肿瘤中，如骨髓增生异常综合征和急性髓系白血病中，观察到STAG2的体细胞突变，并与较差的总生存率和对某些治疗措施更好响应相关。STAG2突变在IDH2突变的白血病患者中普遍存在，并在95%以上的继发性白血病患者中发现。含有STAG2突变的胶质母细胞瘤对PARP的抑制更为敏感。

STAG2 encodes the cohesin subunit SA-2, a component of the cohesin complex that is required for cohesion of the sister chromatids at the centromere after DNA replication in both meiosis and mitosis. Microduplication of the Xq25 chromosome, containing the locus of STAG2, is seen in some types of cohesinopathy that are characterized by abnormal behavior, intellectual disability, distinctive facial appearance and disorders in speech. Inactivating mutations in STAG2 lead to aneuploidy and chromosomal instability in cancer. Nonsense mutations and deletions of STAG2 are found together in melanoma, Ewing sarcoma, glioblastoma, head and neck carcinoma, bladder carcinoma and myeloid neoplasms, whereas deletions alone are observed in gastric, colorectal and prostate cancers. Somatic mutations of STAG2 are observed in myeloid malignancies, such as myelodysplastic syndrome and acute myeloid leukemia, and are associated with worse overall survival and better response to some therapeutic treatments. STAG2 mutations are prevalent in leukemia patients with IDH2 mutations and are found in more than 95% of patients with secondary leukemia. Nonsynonymous mutations are found in glioblastoma, uterine carcinoma and breast carcinoma. Of importance, glioblastomas harboring STAG2 mutations are more sensitive to PARP inhibition.

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