GDNF and growth hormone secreting pituitary adenoma 1: In sporadic somatotroph adenomas, quantitative ARF mRNA expression indicating some remnants of a functional RET-apoptotic pathway, was a significant marker of good prognosis and response to first-line therapy (surgery, somatostatin agonists), while absence of ARF expression indicating exclusivity of RET/GDNF survival pathway was associated to resistance to first-line therapy [30].