KRAS2 mutations in human pancreatic acinar-ductal metaplastic lesions are limited to those with PanIN: implications for the human pancreatic cancer cell of origin

Abstract

Pancreatic intraepithelial neoplasia (PanIN) is a precursor to invasive ductal adenocarcinoma of the pancreas. Observations made in genetically engineered mouse models suggest that the acinar/centroacinar compartment can give rise to ductal neoplasia. To integrate findings in mice and men, we examined human acinar cells, acinar-ductal metaplasia (ADM) lesions, and PanINs for KRAS2 gene mutations. Surgically resected pancreata were screened for foci of ADM with or without an associated PanIN lesion. Stromal cells, acinar cells, ADMs, and PanINs were separately isolated using laser capture microdissection. KRAS2 status was analyzed using genomic DNA isolated from the microdissected tissue. Twelve of these 31 foci of ADM occurred in isolation, whereas 19 were in the same lobules as a PanIN lesion. All 31 microdissected foci of acinar cells were KRAS2 gene wild-type, as were all 12 isolated ADM lesions lacking an associated PanIN. KRAS2 gene mutations were present in 14 of 19 (74%) PanIN lesions and in 12 of the 19 (63%) foci of ADM associated with these PanINs. All ADM lesions with a KRAS2 gene mutation harbored the identical KRAS2 gene mutation found in their associated PanIN lesions. Ductal neoplasms of the human pancreas, as defined by KRAS2 gene mutations, do not appear to arise from acinar cells. Isolated AMD lesions are genetically distinct from those associated with PanINs, and the latter may represent retrograde extension of the neoplastic PanIN cells or less likely are precursors to PanIN.

Figure 1

ADM with (A,C,E) and without (B,D,F) PanINs. A. H&E staining (40x) showing central PanIN lesion (PanIN), ADM (ADM) and acinar cells (AC) in an acinar lobule. B. H&E staining (40X) showing ADM only lesions that are composed of normal duct, metaplastic acinar structures (ADM) and normal acinar cells (AC). C. Higher resolution (100X) of the ADM showing that metaplastic cells contain abundant intracytoplasm mucin, resembling ductal epithelium in the PanIN. D. Higher magnification (100X) of the ADM showing that metaplastic cells are cuboidal cells with minimal mucin. E. Higher resolution (200X) of the interface between the ADM and normal acinar cells. Note that some metaplastic structures are composed of both acinar cells (arrows) and duct-like cells. F. Higher resolution (200X) of the interface between the ADM and normal acinar cells. Note that some metaplastic structures are composed of both acinar cells (arrows) and duct-like cells. Arrows in E and F identify residual acinar cells in partially metaplastic acini.

Figure 2

Representative photographs taken before and after microdissection of ADM lesions with associated PanINs. Photographs before (A) and after (B) microdissection of the PanIN. Representative photographs taken before (C) and after (D) microdissection of the ADM (ADM) in MP16. Note that dissection of the ADM was performed first to prevent potential contamination by the PanIN.

Figure 3

Representative KRAS2 gene sequences, from left-to-right, in the stroma cells, acinar cells, ADM and PanINs. Top row: Representative KRAS2 gene sequences from MP1. Note that the same KRAS2 gene mutation (arrows) is present in both the ADM and PanIN lesion. Middle row: Representative KRAS2 gene sequences from MP16. Note that two KRAS2 gene mutations (GAT and GTT, arrows) are present in the ADM, while only one mutation (GTT) is present in the PanIN. Bottom row: Representative KRAS2 gene sequences from MP15. Note that the KRAS2 gene mutation (CGT, arrow) is only present in the PanIN.

Figure 4

Potential “cell of origin” of pancreatic ductal neoplasia in mouse models and human pancreata. Adapted and reprinted, with permission, from the Annual Review of Pathology: Mechanisms of Disease, Vol. 3, (c)2008 by Annual Reviews www.annualreviews.org(5). Vertical bars indicate the cell of origin as currently established. Backward arrows signify the remaining possibility that the PanIN precursor cell may originate in centroacinar cells.