PIT-1/SF-1 co-expression in pituitary neuroendocrine tumors (PitNETs) with comprehensive review of the literature: How should we best characterize these neoplasms?

The nomenclature and classification of neuroendocrine tumors of the anterior pituitary have undergone significant change over the last few years. Despite the updated classification system as devised by the World Health Organization, some tumors do not fit neatly into the currently defined categories. The most common tumor type not defined by the updated guidelines is a pituitary neuroendocrine tumor with co-expression of SF-1 and PIT-1. In this manuscript, we provide our institutional experience with such unusual cases and combine our findings with those in the available literature to provide the largest, most comprehensive dataset regarding clinical and pathologic information for these unique tumors. Based on our findings, we also propose a classification scheme for pituitary neuroendocrine tumors to integrate lineage, hormonal expression, and clinical function as we believe this constellation of information will best help the clinical teams treating these patients.