In addition, although both phaeochromocytoma and medullary thyroid cancer are major features of MEN 2A and MEN 2B and somatic RET mutations are common in sporadic medullary thyroid cancer (Eng et al, 1994, 1995), somatic RET mutations are found in only 10% of sporadic phaeochromocytomas (Eng et al, 1995; Hofstra et al, 1996). This evidence concerns the gene RET and multiple endocrine neoplasia type 2A.