Autoimmune pancreatitis (AIP) encompasses a heterogenous disease group that includes IgG4-related type 1 AIP and non–IgG4-related type 2 AIP. Clinically and on imaging, type 2 AIP mimics type 1 AIP, other forms of chronic pancreatitis and pancreatic ductal adenocarcinoma (PDAC); therefore, discriminatory markers may aid proper diagnosis. Herein, we examine the expression of PD-L1 and indoleamine 2,3-dioxygenase (IDO1) as a diagnostic tool to distinguish type 2 AIP from other forms of pancreatitis and PDAC.
We evaluated 35 pancreatectomy specimens diagnosed with type 2 AIP and potential mimics of this disease including type 1 AIP (n=14), chronic pancreatitis-not otherwise specified (n=10), groove pancreatitis (n=14), and PDAC (n=278). We scored inflammatory infiltrates, fibrosis and atrophy and performed immunohistochemical staining for PD-L1 and IDO1. We validated our findings on a series of endoscopic ultrasound–guided biopsies from patients with suspected type 2 AIP and inflammatory and neoplastic mimics of this disease (n=37).
The mean age of patients with type 2 AIP was 50 years with a F:M ratio of 1.2:1. Patients with type 2 AIP showed pancreatic ductal staining for PD-L1 and IDO1 in 69% (24/35) and 60% (15/25) of cases, respectively. PD-L1 reactivity was noted in 3% of patients with other forms of chronic pancreatitis and 3% of PDACs; notably, peritumoral ducts and acini were negative. Eight of 9 endoscopic ultrasound–guided biopsies with pancreatic ductal epithelium from patients with type 2 AIP were positive for PD-L1, while the inflammatory and neoplastic mimics were negative. Collectively, the sensitivity and specificity of PD-L1 as a marker of type 2 AIP was 70% and 99%, respectively.
Ductal PD-L1 reactivity has the potential to distinguish type 2 AIP from other forms of pancreatitis and PDAC.
*Department of Pathology, Upstate Medical University, Syracuse, NY
Departments of †Pathology
∥Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA
‡Department of Diagnostic Pathology, Kobe University, Kobe, Japan
§Institute of Liver Studies, King's College Hospital and King’s College London, London, UK
Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article.
Correspondence: Vikram Deshpande, MD, Department of Pathology, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Warren 2, Boston, MA 02478 (e-mail: firstname.lastname@example.org).