SF1 and functioning gonadotropic adenoma: Furthermore, our classification of null cell adenomas was based on negative results of all pituitary hormone on immunohistochemistry; however, the 2017 WHO classification of pituitary adenomas state that the majority of NFPA negative for gonadotrophin staining are, indeed, gonadotroph adenomas when the SF‐1 transcription factor is used and the results may become a little different when analysing this marker.