Beta Cell Adenoma:

A tumor of the beta cells of the islets of Langerhans. Although usually benign, such tumors are among the most important causes of hypoglycemia. Insulinomas usually occur in patients between the ages of 20 and 75 years, the average age being 44-46. Women are 60% of the patients in most series. (Dorland, 27th ed; DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1324)