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Objectives: Pheochromocytoma (pheo) is the second component of the multiple endocrine neoplasia type 2 (MEN 2) syndrome. Clinical expression is sometimes poor, and chronology between medullary thyroid carcinoma (MTC) and pheo is not well evaluated. Therefore, a retrospective study was done in eight European countries in order to precise the main characteristics of pheo in MEN 2., Subjects: Data from 300 MEN 2 patients with pheo (274 MEN 2 A and 26 MEN 2 B) were obtained from cases registered by the EuroMen study group, and collected by a medical standardized questionnaire. These cases occurred between 1969 and 1992., Results: Mean age at diagnosis of pheo was 39.5 years (range 14-68 years) in MEN 2A and 32.4 years (range 15-41 years) in MEN 2B patients. Pheo occurred first in 25.1% of the cases (2-15 years before diagnosis of MTC) and after MTC in 40.2% (2-11 years). In other cases (34.7%), MTC and pheo were diagnosed at the same time. Involvement was bilateral in 67.8% of cases. Malignancy was only 4%. Thirty-nine deaths occurred in these 300 patients, 64.1% were linked in pheo, 23.1% to MTC and 12.8% to other causes. Surgery was unilateral in 39.7% of the cases and bilateral adrenalectomy was the first procedure in 48.4%. A bilateral adrenalectomy in two steps had to be done in 11.9% of cases. In conclusion, these results justify systematic and prolonged biochemical screening of pheo during follow-up of MTC and address some questions about the best mode of surgery.

Multiple endocrine neoplasia type 2A (MEN 2A), type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC) are three dominantly inherited disorders linked to the same disease locus on chromosome 10. Two types of germline mutation of the RET proto-onco-gene, which codes for a transmembrane tyrosine kinase, are associated with MEN 2. Missense mutations at cysteine residues in the extra-cytoplasmic domain are exclusively associated with MEN 2A and FMTC. In MEN 2B patients, a single point mutation at codon 918 has recently been characterized, leading to the replacement of a methionine by a threonine within the RET tyrosine kinase domain. We now report the identification of a mutation at codon 918 in the germline of 16 patients out of 18 unrelated MEN 2B families analyzed. In these families we have been able to demonstrate that, in five cases, the mutation arose de novo, and that, in one kindred, it was coinherited with the disease. These results indicate that a unique mutation at codon 918 of the RET gene is the most prevalent genetic defect causing MEN 2B, but also that rare MEN 2B cases are associated with different mutations yet to be defined.