The morphology of pancreatic endocrine tumors (PETs) is similar to that of 
endocrine tumors elsewhere in the body. PETs are usually encountered in adults. 
They may be clinically functional and associated with various syndromes related 
to hormone excess. However, it must be remembered that absence of obvious 
clinical symptoms may not necessarily reflect true lack of clinical function, 
and subtle clinical manifestations may be missed. Current thinking indicates 
that PETs arise from totipotential stem cells as well as preexisting endocrine 
cells. PETs may be hereditary or sporadic. The hereditary forms are associated 
with multiple endocrine neoplasia type 1 (MEN-1), von Hippel-Lindau syndrome, 
neurofibromatosis, and tuberous sclerosis. In sporadic PETs, the most consistent 
and recurring chromosomal abnormality is allelic loss of chromosome 11q, which 
includes the MEN-1 locus. Loss of a sex chromosome has been shown to be 
associated with metastasis, local invasion, and poor survival.