Understanding Endometrial Cancer
The uterus is a hollow organ located in the female lower abdomen/pelvis, between the bladder and rectum; it serves as the site for fetal development during pregnancy (Vorvick 2012). Uterine tissue, especially that of the inner lining of the uterus, the endometrium, is very dynamic in that it adapts and changes in response to hormonal fluctuations throughout a woman’s menstrual cycle. This manifests as cycles of rapid cellular growth followed by tissue shedding during menstruation (Huang 2012; Rosenblatt 2007).
The endometrium is lined by a thin layer of tightly-packed cells called the epithelium. The endometrial epithelium contains densely-packed epithelial cells and stromal cells (connective tissue) enclosed by two layers of smooth muscle cells (Huang 2012). Epithelial and stromal cells of the endometrium undergo cycles of rapid growth, shedding, and regeneration in response to fluctuating levels of estrogen and progesterone during the menstrual cycle (Rosenblatt 2007; Huang 2012). Sometimes, after many rounds of repeated growth and shedding, genetic changes may occur, leading to alterations in the shape and size of the endometrium. In some cases this causes a thickening of the endometrium, termed endometrial hyperplasia, while in others it can eventually lead to endometrial intraepithelial neoplasia (EIN), which precedes the development of a type of endometrial cancer (Baak 2005; Mutter 2000).
Endometrial cancers can occur in two distinct ways (Duong 2011). Type I endometrial carcinoma, also known as endometrioid endometrial carcinoma, accounts for 70-80% of endometrial cancers, occurs most frequently in pre- and peri-menopausal women, is estrogen dependent, and has a good prognosis if discovered prior to metastasis (spreading of the cancer to other organs or tissues) (Amant 2005; Tao 2010; Duong 2011; El-Sahwi 2012). In contrast, type II carcinoma, also known as non-endometrioid endometrial carcinoma, is most frequent in older postmenopausal women, is not estrogen dependent, is more aggressive, and has a poorer outcome (Duong 2011; El-Sahwi 2012). Women with type II carcinoma tend to be older when the diagnosis is made (Duong 2011). Type II endometrial cancers include uterine clear cell carcinoma, uterine papillary serous carcinoma, and grade 3 endometrioid carcinoma (Hamilton 2006; El-Sahwi 2012; Kim 2013).
If undiscovered, type I and II endometrial carcinomas may eventually metastasize from the endometrium to other parts of the abdomen or elsewhere in the body via the bloodstream or lymphatic system (Amant 2005; The Merck Manual 2013). Once any cancer metastasizes, prognosis worsens.