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Drug Safety Research Laboratory, Taiho Pharmaceutical Co., Ltd., Tokushima, Japan (FN, SS, HT, SH), and Department of Pathology, Faculty of Pharmaceutical Science, Setsunan University, Osaka, Japan (KO, IN)
Abstract
Tumors of the nasal cavity or paranasal sinuses of 18 dogs were examined histopathologically, immunohistochemically, and histochemically. The tumors were classified histologically as 13 adenocarcinomas, 3 transitional carcinomas, 1 squamous cell carcinoma, and 1 adenosquamous carcinoma. Tumor cells were strongly immunoreactive for broad-spectrum cytokeratins in all cases, for cytokeratin 8/18 in 16 cases, and for cytokeratin 19 in 17 cases. None of the 18 carcinomas had cytologic or histologic features indicative of neuroendocrine differentiation, yet tumor cells in 5 of the 13 adenocarcinomas were argyrophilic and immunohistochemically positive for synaptophysin and chromogranin A. Results of this study indicate that neuroendocrine markers may be detected immunohistochemically and histochemically in canine nasal or paranasal adenocarcinomas despite the lack of typical histologic features of neuroendocrine differentiation.
Key words: Adenocarcinoma; dogs; immunohistochemistry; nasal cavity; neuroendocrine differentiation; paranasal sinuses.
Tumors in the nasal cavity or paranasal sinuses are uncommon in dogs.24 Malignant epithelial tumors in these regions are histologically classified as squamous cell carcinoma, transitional carcinoma, adenocarcinoma, adenosquamous carcinoma, adenoid cystic carcinoma, acinic cell carcinoma, undifferentiated carcinoma, olfactory neuroblastoma, and neuroendocrine carcinoma.4 Among these tumors, adenocarcinoma is most common, followed by transitional carcinoma and then squamous cell carcinoma.23 Neuroendocrine carcinomas are rarely reported.16 The main growth patterns of adenocarcinomas are glandular, acinar, papillary, tubulopapillary, and solid. Neuroendocrine carcinomas in the nasal cavity and paranasal sinuses, like those in other regions, are characterized by growth patterns such as sheets, nests, or cords of cells separated by fibrovascular stroma. Tumor cells are small- to medium-sized, round to polyhedral, and have granular eosinophilic cytoplasm.4 Definitive diagnosis of neuroendocrine carcinoma is based on immunohistochemical detection of neuroendocrine markers such as synaptophysin (Syn) and chromogranin A (CgA). Neuroendocrine differentiation has been reported in nasal or paranasal adenocarcinomas in humans,1,8 but not in dogs. Therefore, we examined nasal or paranasal neoplasms of 18 dogs to determine whether malignant epithelial tumors without typical histologic features of neuroendocrine carcinoma expressed neuroendocrine markers by immunohistochemistry and histochemistry.
Materials and Methods
Tumors
All tumors were surgically resected from the nasal cavity or paranasal sinuses of 18 dogs by veterinary practitioners, and formalin-fixed specimens were sent to our laboratory. The dogs consisted of 7 males, 10 females, and 1 of unknown sex; included 7 Shetland Sheepdogs and various other breeds; and were from 8 to 17 years of age. The tumors were located mainly in the nasal cavity or frontal sinus but extended widely from the nasal region to the frontal region (Table 1).
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Immunohistochemistry
Each specimen was stained by the universal immunoenzyme polymer method. The universal staining system (Autostainer, Dako Japan Co. Ltd., Kyoto, Japan) was used for all primary antibodies except cytokeratin (CK) 19. The primary antibodies and antigen retrieval methods are detailed in Table 2.
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Evaluation by immunohistochemistry and histochemistry
The specimens were examined with a light microscope (AX80, Olympus Corp., Tokyo, Japan) and photographed at 400-fold magnification (DP70 and DP control, Olympus Corp.). Positive cells in 5 photomicrographs were counted. The real size of each field was approximately 219 µm x 165 µm. For tumors with multiple growth patterns and pattern-dependent immunohistochemical or histochemical results, examination of 5 fields was performed for each pattern. Immunoreactivity was rated on the following 4-point scale: – (negative), + (< 30% positive cells), ++ (30 to 70% positive cells), +++ (> 70% positive cells).
Results
The tumors were classified as 13 adenocarcinomas, 3 transitional carcinomas, 1 squamous cell carcinoma, and 1 adenosquamous carcinoma (Table 1). The growth patterns in each tumor are presented in Table 3. The predominant growth pattern in adenocarcinomas was tubular (4/13, Fig. 1), tubulopapillary (1/13, Fig. 2), acinar (1/13, Fig. 3), or solid (6/13, Fig. 4). In the remaining adenocarcinoma, tubular and solid patterns were almost equally prominent. Multiple growth patterns were observed in 9 of the 13 adenocarcinomas. The squamous cell carcinoma consisted entirely of a squamous pattern. In the case of the adenosquamous carcinoma, a predominantly squamous pattern was combined with a tubular pattern. All 3 transitional carcinomas had a predominantly stratified pattern that was combined in 1 tumor with a tubular pattern and, in another tumor, with an acinar pattern. None of the 18 cases had a palisading or rosette pattern, suggestive of neuroendocrine differentiation. The cells of the adenocarcinomas had eosinophilic or pale eosinophilic homogeneous cytoplasm and varied in shape (Figs. 1–4). None of these cells had distinctly granular eosinophilic cytoplasm.
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Neuroendocrine carcinomas have been classified separately from epithelial or mesenchymal tumors of nasal or paranasal origin.23 However, cytologic and histologic features of neuroendocrine carcinomas are similar to those in nasal epithelial tumors, and neuroendocrine carcinomas are classified as malignant epithelial tumors in the WHO histologic classification.4 Furthermore, cells that express neuroendocrine markers are occasionally encountered in canine nasal epithelial tumors.
In the present study, although all 18 carcinomas lacked morphologic evidence of neuroendocrine differentiation, 5 of the 13 adenocarcinomas had diffuse or focal immunoreactivity for multiple neuroendocrine markers including Syn, CgA, and argyrophilia by Grimelius' staining. These findings suggested that the 5 adenocarcinomas had neuroendocrine differentiation. Although Syn and CgA are generally used as markers of neuroendocrine tumors, they are not specific for neuroendocrine cells and are also positive in a wide range of tissues, including those of the nervous system. In the present study, we required immunoreactivity for multiple neuroendocrine markers to document neuroendocrine differentiation.
Neuroendocrine carcinomas are malignant epithelial tumors with neuroendocrine differentiation that have been reported in a wide range of tissues, including the liver, bile duct, intestines, paranasal sinuses, lung, and skin of domestic animals.3,5,11,13–15,17,20,21 Sako et al. reported neuroendocrine carcinomas of the nasal cavity in dogs that had typical growth patterns, i.e., sheets, nests, ribbons, or rosette formations, and had cells with eosinophilic cytoplasmic granules.16 In their report, all neuroendocrine carcinomas were CK AE1/AE3–positive, but were negative for CK8 and CK19; some tumors were strongly positive for both Syn and CgA; others were only weakly positive for both neuroendocrine markers or were positive only for CgA.16 A nasopharyngeal neuroendocrine carcinoma in a dog12 had typical neuroendocrine patterns, i.e., groups, sheets, or palisading; tumor cells were negative for CK AE1/AE3 and positive for Syn; immunohistochemistry for CgA was not performed. The neuroendocrine carcinomas in those 2 reports differed in histologic pattern, cytologic features, and CK expression from the adenocarcinomas with neuroendocrine differentiation in the present study.
In humans, adenocarcinomas with neuroendocrine differentiation in the nasal cavity or paranasal sinuses have been reported.1,8 In those reports, CgA and/or Syn were used as markers of neuroendocrine differentiation. The results of the present study are consistent with the immunohistochemical findings for human tumors and indicate that there are adenocarcinomas with neuroendocrine differentiation in the nasal cavity or paranasal sinuses in dogs as in humans. Neuroendocrine differentiation in adenocarcinomas of the nasal cavity or paranasal sinuses was associated with higher mortality in humans.8 Further studies are required to determine whether neuroendocrine differentiation of canine nasal adenocarcinomas warrants a worse prognosis.
Most adenocarcinomas with neuroendocrine differentiation in humans were categorized as intestinal type adenocarcinomas with morphologic characteristics of normal or neoplastic intestinal epithelial cells.1,8 In the present study, however, no correlation between histologic pattern and neuroendocrine differentiation was recognized. The 5 adenocarcinomas with neuroendocrine differentiation had various histologic patterns, including tubular, solid, tubulopapillary, stratified, and acinar. The other 8 adenocarcinomas similarly had no common pattern. On the other hand, tumor cells of the squamous cell carcinoma and squamous regions of the adenocarcinoma or adenosquamous carcinoma were negative for any neuroendocrine markers. This could indicate squamous differentiation and neuroendocrine differentiation are mutually exclusive.
The anatomic structures of the nasal cavity and paranasal sinuses are complicated, especially in dogs.19 The nasal mucosa consists of 4 types of epithelium, namely squamous, transitional, respiratory, and olfactory; the distribution of these epithelia is also complicated.2,9,22 Transition from 1 type of epithelium to another is gradual in nasal mucosa. The nasal epithelium has considerable plasticity in its differentiation in reaction to stimuli.7,10 Neuroendocrine cells are widely scattered in the epithelium of the respiratory tract.6,12,18 The histologic variety of malignant epithelial tumors in the nasal cavity and paranasal sinuses may reflect these anatomic complexities of the nasal mucosa.
Our study demonstrated that some adenocarcinomas in the nasal cavity or paranasal sinuses of dogs undergo neuroendocrine differentiation. However, no correlation between neuroendocrine differentiation and other characteristics of these tumors, such as cytologic features, histologic pattern, proliferation index, tumor location, or signalment of the dogs, was apparent. Thus, the possibility of neuroendocrine differentiation should be considered in nasal adenocarcinomas, even if histologic features of neuroendocrine tumors are not obvious. Grimelius' staining for argyrophilia and immunohistochemical detection of Syn and CgA expression can be used to detect neuroendocrine differentiation in adenocarcinomas without typical histologic features of neuroendocrine tumors.
Acknowledgement
The authors thank Mrs. Hiromi Yanagawa for technical support.
References
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