Fibroadenoma is a type of breast tumor that is not cancerous (benign). These tumors are made up of breast tissue and the tissue that holds breast tissue together (connective tissue). There are several types of fibroadenoma:
Simple fibroadenoma. This is the most common type. This type of tumor consists of a single type of tissue throughout the tumor.
Complex fibroadenoma. This type of tumor contains more than one type of tissue or irregular tissue.
Juvenile fibroadenoma. This is a type of tumor that can develop in adolescent girls. This type tends to grow larger over time than other adenomas.
A fibroadenoma usually occurs as a single lump, but sometimes there may be more than one lump. Fibroadenomas vary in size.