Uterine polyps may be confirmed by an endometrial biopsy, but the biopsy could also miss the polyp. Most uterine polyps are noncancerous (benign). However, some precancerous changes of the uterus (endometrial hyperplasia) or uterine cancers (endometrial carcinomas) appear as uterine polyps.
https://www.mayoclinic.org/diseases-conditions/uterine-polyps/diagnosis-treatment/drc-20378713

