This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
The expression of the following oncogene is associated with a high incidence of Medullary carcinoma of thyroid - 
Select and explain. 
A. P53, B. Her2/neu, C. RET proto-oncogene, D. Rb gene
C: RET proto-oncogene
Answer: C: RET proto-oncogene 
Explanation: RET protooncogene is a growth factor receptor (receptor tyrosine kinase) 
The RET protein is a receptor for the glial cell lined derived neurotrophic factor and structurally related proteins that promote cell survival during neural development.
RET is normally expressed in the following cells


Parafollicular C cells of the thyroid
Adrenal medulla


Parathyroid cell precursors. Point mutation in the RET protooncogenes are associated with the following disorders.

 (i) MEN type 2A -


There is point mutation in RET extracellular domain which causes constitutive dimerization and activation leading to:-
Medullary thyroid carcinoma
Adrenal and parathyroid tumours

(ii) MEN type 2B -
Point mutation in the RET cytoplasmic catalytic domain alter the substrate specificity of the tyrosine kinase and leads to:-
Thyroid tumours
Adrenal tumors
(iii) Sporadic Medullary thyroid carcinoma 

Somatic rearrangement of the RET gene

(iv) Hirschsprung disease

This is caused by complete loss of RET function.