Will having an endometrial biopsy break my hymen?

Unlikely: An endometrial biopsy requires placing a speculum in the vagina. For a virginal woman, it can sometimes be accomplished without disturbing an intact hymen with a very narrow speculum. Many women of the age that would necessitate a biopsy however do not have a narrow intact hymen even if they are virginal.

Probably yes: Because your gyn dr. Will need to insert a vaginal speculum in order to visualise your cervical opening to obtain an endometrial biopsy from the lining of your uterus. Best to discuss this with your gyn dr.