The real explanation of these differences across studies in not fully understood; altogether, the expected results are to detect higher IGF1 and GH levels in GH–PRL PitNETs than in GH PitNETs since most studies describe a larger tumor size in the former [4,95,104], and it is known that, in general, there is a positive correlation between IGF1 levels and tumor size in acromegaly. The gene discussed is PRL; the disease is acromegaly.