Abstract
BACKGROUND: Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are common tumors of the digestive system. Although their histological diagnosis is usually straightforward, the differential diagnosis between neuroendocrine tumors G3 (NET G3) and neuroendocrine carcinomas (NECs) may be challenging at times due to a similar immunophenotype and morphology in a small number of cases. AIMS AND METHODS: The objective of this study was to assess the expression and diagnostic value of PAX5 in GEP-NENs. Immunohistochemical (IHC) analysis for PAX5 was carried out in a large cohort of GEP-NENs, including 39 GEP-NECs and 62 GEP-NETs. RESULTS: Using a semi-quantitative scoring method, PAX5 was shown to be expressed in 30 of 39 GEP-NECs (77%), with 27 of 39 cases (69%) having positivity ≥ 10% in the cells. In particular, GEP-NECs with a high proliferative index had more PAX5-positive cells. None of the cases of GEP-NET G1 and G2 expressed PAX5, while only 2/12 cases of GEP-NET G3 (17%) were positive for PAX5, with PAX5 positivity observed in 1–10% and 10–50% of cells, respectively. The difference in PAX5 expression between GEP-NETs and GEP-NECs was statistically significant (3% vs. 77%, P < 0.001). CONCLUSIONS: PAX5 can be used as a complementary diagnostic IHC marker for GEP-NECs. In addition, PAX5 can be considered in cases when it is difficult to distinguish between GEP-NECs and GEP-NET G3.