GFRA4 and acromegaly: The apparent contradictions related to GFRA4 expression in the altered somatotroph adenomas while it seems not expressed in the normal pituitary, the possibility that GFRα co-receptors can function independently of RET together with the possibility that co-expression of the RET co-receptors could be essential to define stemness in the pituitary drove us to make a comparative study of the four GFRα receptors in the pituitary.