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Introduction
Tubular carcinoid is a rare variant of appendiceal well-differentiated neuroendocrine tumour. Unlike the classic carcinoid tumours of the appendix, tubular carcinoids are characterised by small, widely separated tubules composed of cuboidal to low columnar cells with basally oriented nuclei, indistinct nucleoli and luminal mucin droplets. In addition, they often stain weakly and/or focally for neuroendocrine markers. 1 2 Tubular carcinoids are a biologically distinct form of appendiceal carcinoid tumour and, unlike goblet cell carcinoids, follow a uniformly benign course. However, the small infiltrating tubules that characterise the tumour may on occasion raise concern for metastatic adenocarcinoma.
In the largest study to date, Burke and colleagues reviewed 17 appendiceal tubular carcinoids and demonstrated their unique capacity to express glucagon, whereas the other carcinoids (ie, classic, goblet cell) generally did not. 3 4 Although this finding was substantiated by follow-up studies showing specific expression of glucagon mRNA in tubular carcinoids, 5 other investigators, using a different glucagon antibody, were not able to demonstrate glucagon expression in their cases. 6 Thus, immunostaining for glucagon may not be a reliable method for identifying tubular carcinoids. Furthermore, not all diagnostic pathology laboratories offer glucagon in their immunohistochemistry menus.
Given the paucity of tumour-specific markers for tubular carcinoids, a surgical pathologist may consider using CK7 and CK20 immunostains to help pinpoint the origin of the tumour, if the differential diagnosis includes well-differentiated metastatic adenocarcinoma. However, to date, no study has determined the CK7/CK20 expression profile of appendiceal tubular carcinoids.
Materials and methods
This study was approved by the Johns Hopkins Medicine Institutional Review Board. Hospital electronic pathology files were queried for 'appendiceal carcinoid tumour with tubule formation' or 'tubular carcinoid.' Ten cases were identified from 1991 to 2011: two routine surgical specimens and eight consult cases. Paraffin blocks or unstained slides were available for eight cases. CK7, CK20 and Ki-67 stains were performed according to standard protocols using the following antibodies: CK7 (clone OV-TL, 1:500 dilution; DAKO (Carpinteria, CA, USA)), CK20 (clone Ks20.8, 5 ml prediluted; DAKO) and Ki-67 (clone 30-9, prediluted; Ventana (Tucson, AZ, USA)).
Results
Demographic information
Demographic information is summarised in table 1 . No patients were known to have a history of adenocarcinoma at another body site.
1 | 30 | F | <20 | NA | Ovarian cyst, Appy,... |