An increase in cell production and the cells are slightly abnormal (although they are not cancer cells). Can occur in the breast, womb or other parts of the body. In the breast it is usually diagnosed when a breast lump is tested to see if it is cancerous. It is the only type of benign breast disease that may sometimes develop into breast cancer. So you will probably have the abnormal area removed and may be invited for breast screening more often than other women. In the womb, atypical hyperplasia is also referred to as endometrial hyperplasia and there is detailed information in our cancer question section.