Introduction of immunohistochemical (IHC) analysis of the enzyme aldosterone synthase, encoded by the gene CYP11B2, has made it possible to discern aldosterone production in removed adrenal specimens, thus defining previously unseen aldosterone-producing micronodules [APMs, earlier named aldosterone-producing cell clusters (APCCs)], as well as aldosterone-producing nodules (APNs) and aldosterone-producing adenomas (APAs). This evidence concerns the gene CYP11B2 and adenoma.