Case report 679

Abstract
An infrequently encountered case of well-differentiated CLOS containing dedifferentiated tumor foci in a 28-year-old Japanese man is reported. The patient died from widespread metastases with a microscopic appearance identical to the anaplastic dedifferentiated lesions of the original tumor. This is, to our knowledge, the first report of a case of CLOS with dedifferentiation at the time of initial surgery. The literature concerning CLOS was reviewed and the diagnostic features of CLOS discussed.