Dedifferentiated Endometrial Carcinoma: A Rare Aggressive Neoplasm-Clinical, Morphological and Immunohistochemical Features

SIMPLE SUMMARY: In a neoplasm, dedifferentiation is characterised by the presence of a high-grade neoplasm which can occur de novo, be juxtaposed to, or arise as a recurrence of a previously well-differentiated tumour. Usually, this occurrence results in mesenchymal neoplasms. In epithelial malignant neoplasms, dedifferentiation has been observed in salivary gland carcinomas including adenoid cystic carcinoma, mucoepidermoid carcinoma, myoepithelial carcinoma, and acinic cell carcinoma. In addition, dedifferentiated carcinomas have been reported in the pancreas and in the gastrointestinal and urinary tracts. In the female genital tract, dedifferentiated carcinoma have been described in the endometrium and ovary. Histologically, this entity is characterised by both low-grade endometrioid carcinoma and a solid undifferentiated component. It is especially important to recognise this subtype of the malignancy due to its fulminant clinical outcomes and a poorer prognosis than high-grade endometrioid carcinoma. From a review of the literature, we have extracted clinical, morphological, and immunohistochemical data useful for an accurate diagnosis and prognosis of this rare endometrial malignancy. ABSTRACT: Dedifferentiated endometrioid adenocarcinoma is characterised by the coexistence of an undifferentiated carcinoma and a low-grade endometrioid adenocarcinoma. The low-grade component in this subtype of endometrial carcinoma is Grade 1 or 2 according to the Federation of Gynaecology and Obstetrics (FIGO) grading system. The coexistence of low-grade endometrial carcinoma and solid undifferentiated carcinoma can cause diagnostic problems on histological examination. In fact, this combination can often be mistaken for a more common Grade 2 or Grade 3 endometrial carcinoma. Therefore, this subtype of uterine carcinoma can often go under-recognised. An accurate diagnosis of dedifferentiated endometrial carcinoma is mandatory because of its poorer prognosis compared to Grade 3 endometrial carcinoma, with a solid undifferentiated component that can amount to as much as 20% of the entire tumour. The aim of this review is to provide clinical, immunohistochemical, and molecular data to aid with making an accurate histological diagnosis and to establish whether there are any findings which could have an impact on the prognosis or therapeutic implications of this rare and aggressive uterine neoplasm.