Clinicopathological Correlates of PIT1 and SF1-Multilineage Pituitary Neuroendocrine Tumors and the Diagnostic Utility of NKX2.2 Immunohistochemistry in Pituitary Pathology.

CONTEXT.— PIT1 and SF1-multilineage pituitary neuroendocrine tumors (PitNETs) have been defined since the classification of adenohypophysial tumors based on the PIT1, SF1, and TPIT transcription factors. OBJECTIVE.— To describe the clinicopathologic features of PIT1 and SF1-multilineage PitNETs and to contribute to the pituitary pathology practice by questioning the expression of NKX2.2 in PitNETs. DESIGN.— We reviewed 345 PitNETs and described the clinicopathologic features of 8 PIT1 and SF1-multilineage tumors. NKX2.2 positivity and staining pattern were compared to those of 45 PitNETs from the control group. RESULTS.— PIT1 and SF1-multilineage PitNET patients had a mean age of 41.13 (range, 14-58 years) and a mean diameter of 14.0 mm (range, 8-20 mm). The most common clinical presentation was acromegaly (6 of 8), and postoperative remission was achieved in all patients. On histomorphologic examination, a pseudopapillary pattern was seen in 5 of the tumors, either focally or diffusely. In addition to PIT1 and SF1, there was a diffuse staining with growth hormone and a predominantly perinuclear staining with cytokeratin 18. With NKX2.2, all multilineage tumors were positive, of which 5 were diffuse and 3 were focal. In the control group, 8 tumors (8 of 45) were positive, of which only 1 was diffuse and 7 were focal. CONCLUSIONS.— In conclusion, NKX2.2 is a transcription factor that can be used as an additional tool in pituitary pathology, and PIT1 and SF1-multilineage PitNETs are specific tumors that usually present with acromegaly, show signs of a nonaggressive clinical course, have a pseudopapillary histomorphology, and express NKX2.2.