Endometrial hyperplasia is an overgrowth of endometrial glands, with different shapes and sizes, which causes increased endometrial thickness which results in a greather gland / stroma ratio than observed in normal endometrium. The term endometrial hyperplasia includes different pathologies that have the common feature to increased endometrial thickness. Some of these pathologies have virtually no potential for malignancy while others are clearly premalignant lesions. The pathological diagnosis is the key to the diagnosis of this entity.
Kurman et al (The behavior of endometrial hyperplasia. A long-term study of “untreated” hyperplasia in 170 patients. Kurman RJ, Kaminski PF, Norris HJ. Cancer. 1985 Jul 15;56(2):403-12.) published one of the most important studies describing the evolution of endometrial hyperplasia in which he observed that 1.07% of simple hyperplasia without atypia, 3.4% of the complex hyperplasia without atypia, 8% of the simple hyperplasia with atypia and 23% of the complex with atypia would, if untreated, progress to endometrial cancer. The median time of progression of hyperplasia without atypia to carcinoma has been established in about 10 years, whereas if there is atypia the progression occurs in about 4 years. The presence of atypia is key to the progression to carcinoma.
Also keep in mind that, in case of atypia, there is a 30% chance of an underlying endometrial cancer