Undifferentiated–dedifferentiated endometrial carcinoma; the reappearance of an old friend with insights into the new data

Endometrial carcinoma is a common malignancy in women and shows increasing incidence. Except for its two main pathogenetic types I and II, the continuing evolution on molecular genetics have led to a new classification system (TCGA), that includes four main molecular subtypes: (i) POLE-mutant (ultramutated), (ii) hypermutated (MSI), (iii) copy-number low/MSS (p53wt) and (iv) copy-number high/serous-like (p53mut). The undifferentiated and dedifferentiated endometrial carcinomas are rare and clinically aggressive variants, comprising about 10% of the high-grade endometrial carcinomas and 2% of the endometrial carcinomas in general. Until recently, they were under-recognized and not fully described morphologically and immunohistochemically/molecularly. Their recognition diagnostically is crucial because of their poor prognosis; approximately 40% of patients with these subtypes will die within 0.5-20 months after diagnosis, so additional therapeutic strategies are important for an effective management. Because of their rarity, the responsiveness to other than conventional treatment, such as immunotherapy, has not been sufficiently investigated yet. The aim of this review is to provide an update on the knowledge about these two uncommon subtypes according to the current literature.