The uterus is one of the most important organs in human reproduction, nevertheless its functioning is still poorly understood. A new review of evidence titled “Endometrial Side Population Cells: Potential Adult Stem/Progenitor Cells in Endometrium” published last month in Biology of Reproduction journal tried to describe the big picture of all ongoing research around the physiology of the normal inner lining of the uterus (called endometrium). Medicine has evolved greatly in the last few decades and the importance of basic science laboratory studies cannot be overstated, as they build grounds for clinical (applied) science investigations.

In this review, a team of scientists from Keio University School of Medicine, Japan, described the most current studies on how these cells change and regenerate during each menstrual cycle. Stem cells, cells that can differentiate to various functions and divide (through a process called mitosis), are probably the key to this regenerative function. Changes in the normal functioning of these endometrium cells can give rise to different diseases like endometriosis and endometrial cancer.

Endometriosis is a very frequent condition affecting as much as 10% of reproductive-age women and is caused when endometrium cells begin to grow outside the uterus, usually in the pelvic cavity in the abdomen. The inflammation associated with the cyclic detachment of cells from the wrong site during menstruation is responsible for its symptoms, usually infertility, pelvic pain, painful menstruation and painful sexual intercourse. Endometrial cancer is also the result of the abnormal growth of endometrium cells that can then gain the ability to invade and spread to adjacent tissues and distant parts of the body. Both diseases share some similarities such as the ability of cells to invade and spread. There are actually several studies that explore this resemblance but the two diseases are different in behaviour as cancer ultimately cause death.

The most consensual population of cells thought to be endometrium stem cells is called endometrial side population (ESP), which generate all tissues needed in the normal endometrium throughout its menstrual life cycle. There is an ever-growing body of evidence on these cells and their relationships to the aforementioned diseases is also under research. In the future, this knowledge could be applied to novel treatment approaches and for a possible cure for both endometriosis and endometrial cancer. As the authors state, “the study of ESP cells may provide a breakthrough in understanding of not only the physiology of endometrium but also the phathophysiology of endometrial neoplastic disorders such as endometriosis and endometrial cancer.”