[451] Fixative Type Significantly Affects S100P Immunoreactivity in Fine Needle Aspiration Biopsies of Pancreatic Ductal Neoplasms

RK Pai, KC Jensen, CS Kong. Stanford University, Stanford, CA

Background: Evaluation of pancreatic lesions is frequently based on limited material obtained by fine needle aspiration biopsy (FNAB). S100P has shown promise as an ancillary marker of neoplasia. In this study, we further evaluate the utility of S100P in distinguishing benign epithelium from ductal neoplasms in FNAB and specifically evaluate the effect of fixative solution.
Design: A tissue microarray (TMA) study set of 321 resections consisted of 77 ductal adenocarcinoma (PDAC), 73 benign pancreas, 50 intraductal papillary mucinous neoplasm (IPMN), 20 mucinous cystic neoplasm (MCN), and 36 PanIN, as well as 61 normal small intestine and stomach. A test set of paraffin-embedded cell block material from 57 FNAB included 42 PDAC (16 confirmed on resection), 4 atypical cases (confirmed as PDAC on resection), 2 mucinous neoplasms (confirmed on resection), and 9 benign ductal epithelium. S100P immunohistochemistry (BD Biosciences, clone 16) was performed and scored as negative (no staining), 1+ (1-25%), 2+ (25-75%), and 3+ (>75%).
Results: In the study set, 70/73 PDAC exhibited 3+ S100P. 1/73 benign pancreas exhibited 1+ S100P. IPMN (50/50), MCN (18/20), and PanIN (36/36) exhibited 3+ S100P reactivity. Compared with benign pancreas, S100P was 99% sensitive and 99% specific for ductal neoplasms. 19/20 normal gastric mucosa demonstrated 3+ S100P while normal small bowel was S100P negative (0/27). S100P labeled 29/42 (69%) PDAC, 4/4 of atypical cases, and 2/2 mucinous neoplasms (Table 1). Compared with benign pancreas, S100P was 72% sensitive and 100% specific for ductal neoplasms. Cytolyte-fixed material from pancreatic neoplasms was less often S100P-positive (20/32) compared with formalin-fixed tissue (14/15) (p=0.03). S100P was positive in 8/19 gastrointestinal mucosa from EUS-FNAB.

Table 1. S100P Immunohistochemistry in FNAB Test Set
Cytologic FindingsNo. of CasesS100P NegativeS100P 1+S100P 2+S100P 3+Cytolyte Fixative (Pos/Total)Formalin Fixative (Pos/Total)
Mucinous Neoplasm201011/11/1
Benign Ductal Cells990000/30/6
Gastrointestinal Mucosa19111344/134/6

Conclusions: S100P is a sensitive marker of ductal neoplasia in the pancreas, but cannot distinguish between PDAC and its precursors. S100P cannot distinguish between mucinous neoplasia and gastric mucosal sampling in EUS-FNAB. For optimal results, specimens should be fixed in formalin and not cytolyte.
Category: Cytopathology

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 44, Wednesday Afternoon


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