3670

ISL1

ISL LIM homeobox 1;ISL1;ISL LIM homeobox 1

ISL1 transcription factor, LIM/homeodomain|insulin gene enhancer protein ISL-1|islet-1

5q11.1

protein-coding

Neuroendocrine tumors can present as liver metastases before discovery of the primary tumor. Islet 1 and PAX8 have recently been proposed as markers for neuroendocrine tumors of pancreatic origin. In this study, we compared the utility of Islet 1 and PAX8 in distinguishing pancreatic neuroendocrine tumors from neuroendocrine tumors of other sites and determined the usefulness of an immunohistochemical panel, including TTF1, CDX2, Islet 1 and/or PAX8, in identifying metastatic pancreatic neuroendocrine tumors. A total of 110 primary neuroendocrine tumors (33 pancreatic, 31 pulmonary, 23 ileal, 14 rectal, and 9 gastric) and 73 metastatic neuroendocrine tumors (28 pancreatic, 5 pulmonary, 37 ileal, 1 rectal, 1 colonic, and 1 duodenal) were studied. Islet 1 and PAX8 were positive in 27/33 (82%) and 29/33 (88%), respectively, of primary pancreatic neuroendocrine tumors, and in 19/28 (68%) and 15/28 (54%), respectively, of metastatic pancreatic neuroendocrine tumors. No cases of primary (0/23) or metastatic (0/37) ileal neuroendocrine tumors were positive with either Islet 1 or PAX8. There was Islet 1 positivity in 2/31 (6%) primary pulmonary, 12/14 (86%) primary rectal, and 1/1 metastatic rectal neuroendocrine tumors, and PAX8 positivity in 7/31 (23%) primary pulmonary, 11/14 (79%) primary rectal, and 2/9 (22%) primary gastric neuroendocrine tumors. ROC curve analysis incorporating sensitivity and specificity data of immunohistochemical panels for metastatic pancreatic neuroendocrine tumors showed that a four-stain panel, including Islet 1, PAX8, TTF1, and CDX2 significantly outperformed a three-stain panel composed of PAX8, TTF1, and CDX2 (P=0.019), and also showed a trend for better performance compared with a three-stain panel composed of Islet 1, TTF1, and CDX2 (P=0.072). Both Islet 1 and PAX8 are reliable immunohistochemical markers for pancreatic neuroendocrine tumors and would be useful adjuncts to other markers (TTF1, CDX2) currently used to work up a metastatic neuroendocrine tumor of unknown primary.

Islet-1 (Isl1) is a transcription factor involved in the embryogenesis of islets of Langerhans. Immunohistochemically, Isl1 is a sensitive lineage-specific marker for pancreatic neuroendocrine neoplasms (NENs) and their metastases. Its specificity has not been documented, nor have large numbers of NENs from other parts of the gut or other organs been studied. We examined Isl1 expression in 203 primary NENs (gastroenteropancreatic, lung, breast, and ovarian neoplasms) and 40 hepatic NEN metastases (enteropancreatic and lung neoplasms) from known primaries. The correlation between Isl1 and CDX2 expression was studied using a tissue microarray containing 46 pancreatic NENs. Immunostaining for Isl1 and CDX2 was also performed in selected NENs from other sites. Isl1 was positive in 90% of pancreatic, 89% of duodenal, 100% of rectal, 38% of colonic, 14% of appendiceal, and 6% of ileal primaries. Isl1 was negative in all other NENs. Among metastatic neoplasms, 76% of pancreatic and 2 of 2 rectal NEN metastases were Isl1 positive, whereas all other tested metastases were negative. The overall sensitivity and specificity of Isl1 in identifying primary pancreatic NENs was 88% and 80%, respectively. Thirty-six of 46 pancreatic NENs in the tissue microarray were Isl1 positive; 4 were Isl1 negative but CDX2 positive. Our findings confirm that Isl1 is a sensitive marker of pancreatic origin in cases of metastatic NEN. However, Isl1 does not distinguish pancreatic NEN from duodenal and colorectal NEN, even when used in association with CDX2.