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immunohistochemistry; moustached tamarin; pulmonary cystadenoma; surfactant proteinsCystadenomas are epithelial tumours that are formed by the cystic dilation of secretory glandular epithelial units and may arise in multiple organs. Cystadenomas are subclassified by their form (e.g. serous, papillary or mucinous) or by their location (e.g. bile duct, endometrium, appendix or pancreas). Mucinous cystadenoma is a tumour that forms a uni- or multilocular mass lined by well-differentiated cuboidal to columnar mucus-producing epithelium (Head and Else, 2002; Gao and Urbanski, 2005). The World Health Organization defines mucinous cystadenoma as a localized cystic mass filled with mucin and surrounded by a fibrous wall lined by well-differentiated columnar mucinous epithelium (Travis et al., 2004). Mucinous cystadenomas have been described in the parotid gland (Head and Else, 2002) and gall bladder in cats (Cullen and Popp, 2002) and in the ovary of a cow (García-Iglesias et al., 1991) and a cynomolgus macaque (Sato et al., 2008). There are no reports of the mucinous form of cystadenoma in the lungs of mammals other than man. This report describes a mucinous cystadenoma in the lung of a non-human primate.A 2-year-old, male, captive-born, moustached tamarin (Saguinus mystax) was part of a study into viral hepatitis that was approved by the Institutional Animal Care and Use Committee and was completed at the time of the animal's death. The tamarin was pair-housed with a female, in accordance with advice and regulations ( Institute for Laboratory Animal Research, 1996). The tamarin was found dead on morning rounds and a complete necropsy examination was performed. The carcass was in good bodily condition. A single large area of haemorrhage was noted at the base of the skull. This lesion was indicative of compression head trauma, which was ruled as the cause of death and attributed to cage-mate fighting. An incidental finding was a round, well-demarcated, subpleural, circumscribed mass (0.6 cm diameter) in the distal portion of the right caudal lung lobe. Tissue samples were collected from all major organs and fixed in 10% neutral buffered formalin. Following routine processing and embedding in paraffin wax, sections were stained with haematoxylin and eosin (HE). Sections of the lung mass were also stained with periodic acid–Schiff (PAS) with and without diastase digestion, alcian blue (pH 2.5), toluidine blue, Mayer's mucicarmine, Gram, Masson's trichrome (MT) and elastic Van Gieson stains.Immunohistochemistry (IHC) was performed as described by Michaud et al. (2012) using antibodies against surfactant protein (SP)-A (Millipore, Temecula, California, USA; rabbit polyclonal antibody reactive with human, mouse, rat and primate SP-A; dilution 1 in 500), SP-B (Abcam, Cambridge, Massachusetts, USA; rabbit polyclonal antibody reactive with mouse, sheep, cow and human SP-B; dilution 1 in 500), SP-C (Abcam; rabbit polyclonal antibody reactive with human and mouse SP-C; dilution 1 in 100) and SP-D (Abcam; biotinylated mouse monoclonal antibody specific for human and rat SP-D; clone IIE11; dilution 1 in 40). Positive and negative controls were used in each experiment.Microscopically, the mass was well-circumscribed and non-encapsulated, located within the subpleural space, causing a nodular expansion and compressing the adjacent lung parenchyma with no evident invasive growth (Fig. 1). The mass was composed of randomly-arranged cystic spaces, which were up to 40 times the size of non-neoplastic lung alveoli, lined mostly by a single layer of columnar to lower cuboidal mucus-secreting epithelial cells, with occasional small papillary projections into the lumen. The mucus-producing cells had a single round to polygonal basally-oriented nucleus, containing up to two densely basophilic nucleoli and had a stippled chromatin pattern with minimal atypia and no mitotic figures. In some cells, the nuclei were hyperchromatic and homogeneous. Few areas with cells undergoing apoptosis were observed in the epithelium lining the cystic spaces. The branching trabecular stroma that supported and divided the mass into cystic spaces was variably attenuated, often composed of spindle-shaped cells with an elongated thin nucleus, loose connective tissue, some medium-sized blood vessels and infiltrates of low numbers of lymphocytes and plasma cells in some areas; however, some trabeculae consisted of only a monolayer of cuboidal to flattened cells resembling interalveolar septa and lacking the lining of mucus-producing cells (Fig. 2). The cystic spaces within the mass were filled with an eosinophilic, granular material that was loosely arranged in whorls, cell remnants and variable numbers of foamy macrophages. Masson's trichrome staining demonstrated mucin within the cystic spaces and minimal stromal collagen. The granular material was PAS positive and diastase resistant (Fig. 3), displaying positive reaction with the alcian blue and Mayer's mucicarmine stains. A discrete area at the periphery of the mass showed extension of this material towards the adjacent normal lung parenchyma (Fig. 1). None of the SPs were expressed immunohistochemically by the neoplastic epithelium. A discrete and small area in the middle of the tumour reacted strongly with antibody to SP-B, suggesting trapped surfactant (Fig. 4). The normal adjacent lung parenchyma displayed SP-A, SP-B, SP-C and SP-D in type II pneumocytes and alveolar macrophages, in addition to a free form of surfactant containing these four SPs that lined the alveolar spaces.
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