Original contributionCD133 expression in well-differentiated pancreatic neuroendocrine tumors: a potential predictor of progressive clinical courses☆
Introduction
Pancreatic neuroendocrine neoplasms are rare and only account for between 1% and 3% of primary pancreatic tumors [1]. They have been classified into pancreatic neuroendocrine tumors (PanNETs) and neuroendocrine carcinomas with distinct pathological features. The former (World Health Organization [WHO] grades 1 and 2 [G1 and G2]) are characterized by relatively uniform tumor cells arranged in a trabecular and solid architecture, whereas the latter (WHO grade 3 [G3]) show high-grade morphologic features resembling small cell carcinomas or large cell neuroendocrine carcinomas of the lungs [1], [2]. G1 and G2 neoplasms are also often referred to as well-differentiated PanNETs. One clinical challenge is to predict the biological behavior of well-differentiated PanNETs. The single reproducible histologic predictor is proliferative activity estimated by mitotic counts and Ki-67 indices. G1 neoplasms show less than 2 mitotic counts (per 10 high-power fields) and a Ki-67 labeling index of 3% or less, whereas G2 is defined as having at least 2 to 20 mitotic counts or a Ki-67 index of 3% to 20% [3]. However, because these criteria are not sufficient to predict clinical courses, other standards that may be used in combination with the WHO grades are awaited.
The aims of some pathological studies have been to identify ancillary immunohistochemical markers to grade PanNETs. Among the potential prognostic markers proposed to date (eg, COX2, p27, and CD99) [4], [5], [6], CK19 has been the most extensively studied in this aspect [7], [8], [9], [10], [11], [12], [13]. CK19 was found to be positive in between 49% and 70% of PanNETs, with its expression being associated with aggressive pathological features (eg, higher mitotic counts, lymphovascular invasion, and higher TNM stages) [7], [8], [9], [10], [11], [12], [13]. Cancer-related death occurred in 36% of the CK19+ cases (10/28) and none of the CK19− cases (0/26) examined in an index report [7]. Three studies confirmed that CK19+ cases had a significantly poorer prognosis [9], [10], [11], whereas another 2 did not validate this finding [12], [13]. Another potential prognostic marker is KIT, which was shown to be expressed in between 8% and 46% of PanNETs, with its relevance to a poor prognosis being indicated in 2 studies [10], [13]. CK19 and KIT both appear to be expressed in endocrine cells of the embryonic pancreas, but not in matured islets [14], [15], [16], suggesting that an immature or stem cell phenotype in PanNETs is linked to an aggressive biological behavior and poorer prognosis, similar to many other malignant neoplasms of the extrapancreatic organs.
CD133 (also called prominin-1), encoded by the PROM1 gene (4p15.32), is a widely accepted stem cell marker [17]. It was originally discovered from neural progenitors and hematopoietic stem cells, and its expression was further confirmed in the stem cells of other cellular lineages [18], [19], [20]. Because the expression of CD133 has also been detected in malignant neoplasms, it has been used to isolate a principal subset of cells (“cancer stem cells”) either alone or in combination with other markers [21]. In the pancreas, ductal adenocarcinomas were mainly investigated from the aspect of CD133 expression [22], [23]. However, CD133 expression in PanNETs has not yet been examined. One previous study examined CD133 expression in 90 neuroendocrine neoplasms of the digestive system [24]. One case each of pancreatic neuroendocrine carcinoma (WHO G3) and mixed acinar-neuroendocrine carcinoma was included in the study cohort, but no case of G1 or G2 PanNET was studied.
In the present study, we examined CD133 expression in well-differentiated PanNETs using 2 separate cohorts, and correlated the results obtained with other clinicopathological features to elucidate the prognostic value of CD133 expression in this uncommon pancreatic neoplasm.
Section snippets
Study cohorts
This study was approved by the ethics committee at Kobe University Graduate School of Medicine (No. 1794). The study consisted of 2 independent cohorts. The first was a consecutive series (n = 178) of well-differentiated PanNETs that were surgically resected at Asan Medical Center in Seoul between 1995 and 2013. In these cases, tissue microarrays had already been constructed and used in previous studies [13], [25]. Tissue arrays contained 3 cores (2 mm in diameter) from each tumor. Although
The discovery cohort
Fourteen (8%) of the 174 PanNETs examined were immunoreactive to CD133. Of the 3 tissue cores available for each case, all 3 were positive in 8 cases, 2 cores in 5 cases, and only 1 in 1 case. In CD133+ PanNETs, CD133 was strongly expressed on the cell membrane with slightly weaker cytoplasmic staining (Fig. 1A, arrow and arrowhead, respectively), whereas in cases of CD133− PanNET, CD133 immunostaining marked entrapped nonneoplastic ducts (Fig. 1B, asterisk). The clinicopathological features of
Discussion
The results of the present study suggest that CD133 is expressed in up to 20% of well-differentiated PanNETs, and its expression may be related to progressive clinical courses. CD133 expression was associated with unfavorable pathological findings such as a large tumor size, lymphovascular invasion, and/or perineural infiltration. CD133+ PanNETs were more advanced at the time of surgery (higher TNM stages) and showed shorter disease-free periods. The expression of CD133 continued to be
Acknowledgments
Author contributions
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Sakai Y., An S., Kim J. Y., Otani K., Fujikura K., Hirose T., and Itoh T.: histologic analysis, clinicopathological relationships, interpretation of data, drafting the manuscript
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D. Corbeil and J. Karbanová: study design, interpretation of data, drafting the manuscript
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Song K.-B., Kim S. C., Akita M., Nanno Y., Toyama H., Fukumoto T., and Ku Y.: tissue sampling, analysis of clinical features, drafting the manuscript
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Hong S.-M. and Zen Y.: study design, histologic analysis,
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Disclosures: None to disclose.