Which of the following endocrine tumors is most commonly seen in MEN I?
"Most common neuroendocrine tumour associated with MEN I is Gastrinoma."

MEN -1 is also called werner syndrome.
It is characterized by abnormalities involving the

- Parathyroid
- Pancreas
- And Pituitary gland thus the mnemonic device the "3 Ps".
Parathyroid

Primary hyperparathyroidism is the most common manifestation of MEN I (80% to 90%) of patients.
It is the initial manifestation of the disorder in most patients appearing in almost all patients by the age of 40 to 50.
Parathyroid abnormality includes both adenoma and hyperplasia.
Hypercalcemia occurs due to hyperparathyroidism.


Pancreas 

Pancreatic islet cell tumours are the 2nd most common abnormalities in MEN I syndrome.
Gastrinoma is the most common enteropancreatic tumour observed in MEN I.
Insulinoma are second most common enteropancreation tumour in MEN I.

Pituitary

Most frequent anterior pituitary tumour encountered in MEN I is prolactinoma.

Also remember these important facts about MEN I syndrome -

MEN I syndrome is caused by germ line mutations in MEN I gene at 11q13.
MEN I is a classic tumour suppressor gene.
The dominant clinical manifestations of MENI are due to peptide hormones overproduction such as Zollinger Ellison syndrome due to gastrinoma and recurrent hypoglycemia. Hypercalcemia can result due to hyperparathyroidism.
Insulinoma
Gastrinoma
Glucagonoma
Somatostatinoma