The Multiple Endocrine Neoplasia Syndromes

There are at least three distinct syndromes that feature hyper- or neoplasia of the endocrine glands, termed appropriately enough, multiple endocrine neoplasia (MEN), types I-III[1]. The former designation of multiple endocrine adenoma syndrome is also used, but it implies that the conditions are inherently benign, which is clearly not true, and for this reason, substitution of neoplasia for adenoma is more accurate. Since types II and III have certain features in common, some prefer a IIa and IIb designation. However, as will be shown, the two conditions differ from one another substantially enough that the former enumeration seems more appropriate. There are also ‘overlap’ patients whose clinical characteristics may be shared by more than one of the MEN syndromes. Usually these are isolated instances that prove or disprove nothing in regard to the relationship between the established MEN syndromes, either from a genetic or an etiologic point of view. A few of these endocrine tumor associations can be explained on the basis of a common embryologic origin of the tissues in question or a common exposure to a given environmental insult. In other instances, the reason for the assocation is not at all apparent. Some may actually be due to chance, while others may result from as yet poorly defined gene defects; i.e., it is quite possible and even likely that additional MEN syndromes exist.