S1440 A Case Series of Five Solid Pseudopapillary Neoplasm of Pancreas: Comparison of Four Putative Immunohistochemical Stains With Four Conventional Immunohistochemical Stains

Abstract

INTRODUCTION: Solid pseudopapillary neoplasm (SPN), a rare exocrine tumor, accounts for 0.2-2.7% of primary pancreatic tumors occurs mostly in young females. The histologic origin is debatable and thus, it is important to identify the most sensitive and specific biomarkers. Through this case series, we are addressing the comparative analysis of four commonly used immunostains with 4 new putative immunohistochemical markers. CASE DESCRIPTION/METHODS: We performed an electronic search of pathology records for a 25 years-period (1994-2019) for SPN. Formalin-fixed, paraffin-embedded tissue blocks were retrieved and used for staining for four commonly used (CD-10, Beta- Catenin, Progesterone receptor, Alpha-1 antitrypsin) and four new (LEF-1, TFE-3, SOX-11 and AMACR) immunohistochemical markers.: In our case-series, female-to-male ratio is 4:1, with a mean age of 37.6 years. The tumor size ranged from 2.3 to 14 cm. Only one case showed aggressive features of necrosis, perineural invasion and lymphovascular invasion. None of the cases showed lymph node or distant metastasis. The results from the immunohistochemical staining are noted in Table 1. DISCUSSION: In our case series, lymphoid enhancer factor-1 (LEF-1) emerged out as the most sensitive new putative marker with 100% diffuse nuclear positivity among the other new markers. To the best of our knowledge, these novel results are noted for the first time in our case series. This significant finding is in congruence with the emerging molecular diagnostic finding that the long isoform of LEF-1 expresses b-catenin binding domain and functions as a transcriptional enhancer factor. It also emphasizes the involvement of Wnt/β-catenin signaling pathway in the histologic origin of this tumor. Further studies are needed to evaluate its specificity especially against SPN mimickers such as Acinar-cell carcinoma and pancreatic neuroendocrine tumors.Figure 1.: Figure 1: A. Solid pseudopapillary neoplasm H&E section at 200x. B. SPN TFE-3 stain at 200x C. SPN Alpha 1 antitrypsin 200x D. SPN AMACR stain at 400x E. SPN Beta Catenin at 400x F. SPN CD10 at 400x G. SPN LEF-1 stain at 400x H. SPN SOX-11 stain at 400x.Table 1.: Staining pattern and comparison of four conventional stains with 4 putative stains in 5 cases of Solid Pseudopapillary neoplasm of pancreas.