Current data from several groups have demonstrated that macroH2A1 plays important roles in both tumor suppression and differentiation, and the alteration in macroH2A1 splicing and expression occurs in a variety of cancers, including testicular, lung, urinary bladder, cervical, breast, colon, ovarian, and endometrial cancers [16–18]. The gene discussed is MACROH2A1; the disease is endometrial cancer.