Overexpression of lymphoid enhancer-binding factor 1 (LEF1) in solid-pseudopapillary neoplasms of the pancreas

Abstract

Solid-pseudopapillary neoplasms are rare, but are distinctive pancreatic tumors of low-malignant potential. While the histogenesis of these tumors is unclear, they are often associated with gain-of-function mutations in the catenin (cadherin-associated protein), beta 1 (88 kDa), or CTNNB1 gene, resulting in nuclear accumulation of CTNNB1. CTNNB1 is a central component of the Wnt signaling pathway and mediates gene expression through the lymphoid enhancer-binding factor 1 (LEF1) /T-cell factor transcription complex. Although LEF1 has a pivotal role in the transactivation of Wnt/CTNNB1 responsive genes, the status of LEF1 in solid-pseudopapillary neoplasms and other pancreatic tumors has not been examined. We analyzed both LEF1 and CTNNB1 in a large cohort of pancreatic tumors (n=155). In all cases of solid-pseudopapillary neoplasms including surgical resections (n=27) and cytologic samples (n=8) had strong and diffuse nuclear labeling for both LEF1 and CTNNB1. The surrounding uninvolved pancreatic parenchyma was devoid of any LEF1 staining. All resection and cytologic specimens from well-differentiated pancreatic neuroendocrine tumors (n=44; n=29, respectively), high-grade pancreatic neuroendocrine carcinomas (n=2; n=1), pancreatic ductal adenocarcinomas (n=25; n=12), and acinar cell carcinomas (n=9; n=2) studied were negative for both nuclear LEF1 and CTNNB1. However, nuclear LEF1 and CTNNB1 were detected in all four resected pancreatoblastomas (no cytologic specimens were available for immunolabeling), but primarily centered around and within squamoid corpuscles. In summary, abnormal CTNNB1 accumulation was accompanied by nuclear LEF1 overexpression in both solid-pseudopapillary neoplasms and pancreatoblastomas. But, in contrast to pancreatoblastomas, a diffuse, nuclear labeling was observed in solid-pseudopapillary neoplasms and further implicates the CTNNB1/LEF1 transcriptional complex in the development of solid-pseudopapillary neoplasms. In addition, as part of an immunohistochemical panel, LEF1 can be a useful ancillary stain in the diagnosis of solid-pseudopapillary neoplasms.

Figure 1

Immunohistochemical staining for LEF1 and CTNNB1 in normal pancreatic parenchyma (a, H&E, ×200) and solid-pseudopapillary neoplasms (b, H&E, ×200). The normal pancreatic parenchyma including endocrine and exocrine components is negative for LEF1 (c, ×200) and shows a membranous staining pattern for CTNNB1 (d, ×200). In contrast, a strong and diffuse nuclear labeling for LEF1 (e, ×200) and abnormal nuclear and cytoplasmic CTNNB1 accumulation (f, ×200) are observed with solid-pseudopapillary neoplasms.

Figure 2

At high magnification, solid-pseudopapillary neoplasms are composed of loosely cohesive cells surrounded by delicate capillaries and interspersed macrophages (a, H&E, ×400). Immunohistochemical stains for LEF1 are diffusely positive within the tumor nuclei, but negative within endothelial cells and macrophages (b, ×400). CTNNB1 shows a membranous staining in both the neoplastic and nonneoplastic components of the tumor; however, nuclear and cytoplasmic accumulation is only seen in the neoplastic cells (c, ×400). In comparison, membranous labeling for E-cadherin is lost within the tumor cells, while retained in the intervening macrophages. Patchy CD10 (e, ×400) and paranuclear dot-like CD99 (f, ×600) staining were also seen within the tumors.

Figure 3

Cytologic cell blocks from solid-pseudopapillary neoplasms often show small, uniform, individual cells with bland nuclei (a, H&E ×400). Both LEF1 (b, ×400) and CTNNB1 immunohistochemical stains demonstrate nuclear positivity. However, during cell block preparation, the tumor cell membranes may be disrupted. This results in a dispersed cytoplasmic staining of CTNNB1, which can impede nuclear interpretation (c, ×400). Similarly, paranuclear dot-like CD99 staining can be difficult to identify (d, ×600) and in some cases be negative.

Figure 4

Well-differentiated pancreatic neuroendocrine tumors (a (H&E) and b (immunohistochemical stains), ×200), acinar cell carcinomas (c and d), and pancreatic ductal adenocarcinomas (g and h) were negative for LEF1 (left panel) and showed membranous staining for CTNNB1 (right panel). In contrast, nuclear LEF1 and CTNNB1 staining was detected in pancreatoblastomas, but primarily centered around and within squamoid corpuscles including tumor cells with optically clear nuclei (e and f).