We aimed to classify undifferentiated/dedifferentiated carcinoma (UDC/DDC) according to the four TCGA molecular subgroups of endometrial cancer: microsatellite-instable/hypermutated (MSI), POLE-mutant/ultramutated (POLE), copy-number-low/p53-wild-type (p53wt), and copy-number-high/p53-abnormal (p53abn), through a systematic review and meta-analysis. Electronic databases were searched from January 2013 to July 2019 for studies assessing the TCGA classification in endometrial UDC/DDC series. Pooled prevalence of each TCGA subgroup on the total UDC/DDCs was calculated. Three studies with 73 patients were included. Pooled prevalence of the TCGA subgroups were: 12.4% for the POLE subgroup, 44% for the MSI subgroup, 18.6% for the p53abn subgroup, 25% for the p53wt group. All TCGA groups are represented in UDC/DDC, with a predominance of the MSI group, indicating a biological heterogeneity. Hypermutated/ultramutated cancers constitute the majority of UDC/DDC, suggesting a crucial difference with other high-risk histologies of endometrial carcinoma.