Endometrioid
endometrial carcinoma has an overall good prognosis. However, variable five-year survival rates (92%-42%) have been reported in FIGO stage I, suggesting the involvement of other factors related to
tumor biological behavior. These may be related to the role played by epithelial-mesenchymal transition (EMT) and cancer stem cells in endometrial
carcinogenesis. In this context, our review highlights the prognostic significance of several types of myoinvasion in low grade, low stage endometrioid
endometrial carcinoma, as a reflection of these molecular changes at the invasive front. According to recently introduced myoinvasive patterns, the diffusely infiltrating and microcystic, elongated, and fragmented (MELF) patterns show loss of
hormone receptors, along with EMT and high expression of cancer stem cell markers, being associated with a poor prognosis. Additionally, MELF pattern exhibits a high incidence of lymphovascular invasion and
lymph node metastases. Conversely, the broad front pattern has a good prognosis and a low expression of EMT and stem cells markers. Similarly, the
adenomyosis (AM)-like and
adenoma malignum patterns of invasion are associated to a favorable prognosis, but nevertheless, they raise diagnostic challenges. AM-like pattern must be differentiated from
carcinoma invasion of AM foci, while
adenoma malignum pattern creates difficulties in appreciating the depth of myoinvasion and requires differential diagnosis with other conditions. Another pattern expecting its validation and prognostic significance value is the nodular
fasciitis-like stroma and large cystic growth pattern. In practice, the knowledge of these patterns of myoinvasion may be valuable for the correct assessment of stage, may improve prognosis evaluation and may help identify molecules for future targeted
therapies.