This common chronic condition — where tissue similar to what grows inside the uterus grows elsewhere in the body — is barely understood. So why is a condition so prevalent and painful still so unknown? It has a lot to do with who gets to ask research questions.

Correction, August 18: An earlier version of this episode implied that the tissue involved in endometriosis is the same as the endometrium, which lines the uterus. It is similar tissue, but not identical.

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