Spontaneous basaloid adenomas of the mammary gland in four dogs: clinicopathologic and immunohistochemical features

Spontaneous basaloid adenomas occurred in four out of 354 dogs with mammary tumors. Affected dogs were pure-bred, intact females between 6 and 8 years of age. Three dogs were nuliparous, two had pseudopregnancies, and none had received contraceptive steroids. The tumors were multiple (three cases) or unique, less than 1 cm in diameter, well delineated, and composed of uniform cords and clusters of monomorphic epithelial cells with focal signs of squamous or glandular differentiation. A basal cell immunophenotype (cytokeratins 5 and 14 positive) without either glandular epithelial (cytokeratins 8, 18, and 19 negative) or myoepithelial (calponin negative) differentiation was observed in the majority of tumor cells. No recurrence or metastasis was recorded after follow-up periods between 3 and 24 months. In spite of the hormone-dependent nature of this tumor in female Beagles given experimental contraceptive steroids, spontaneous basaloid adenomas lacked estrogen receptor alpha and progesterone receptors.     

The expression of p63 and cytokeratin 5 in mixed tumors of the canine mammary gland provides new insights into the histogenesis of these neoplasms

Cytokeratin 5 and p63 have been described as basal and myoepithelial cell markers in human breast. Mixed tumors of the canine mammary gland have been associated with a myoepithelial origin. Cytokeratin 5 expression has not been evaluated in these tumors. We investigated the relation between cytokeratin 5 and p63 double-immunohistochemical expression in 23 mixed tumors of the canine mammary gland (10 benign mixed tumors and 13 carcinomas arising from benign mixed tumors) and their origin. Cytokeratin 5 and p63 co-expression was observed in myoepithelial cells of benign mixed tumors, as well as in squamous differentiation of carcinoma arising from benign mixed tumors. Though a few interstitial spindle cells of the mesenchymal components expressed both p63 and cytokeratin 5, the basal epithelial cells were labeled only by cytokeratin 5. The co-expression of p63 and cytokeratin 5 in myoepithelial cells and squamous differentiation suggest that, like in human breast, cytokeratin 5 can also be considered a myoepithelial- and squamous-cell differentiating marker in canine tumors. The presence of some interstitial spindle cells stained for p63 and cytokeratin 5 might be associated with a myoepithelial origin of the mesenchymal component of mixed tumors of the canine mammary gland. Moreover, contrary to p63, basal epithelial cells were labeled by cytokeratin 5, indicating that cytokeratin 5 may not represent an exclusive myoepithelial cell marker but also a basal epithelial cell marker in canine mixed tumors. According to these data, basal epithelial cells may be related to the origin of the epithelial component of mixed tumors of the canine mammary gland.     

p63: a novel myoepithelial cell marker in canine mammary tissues

Several immunohistochemical markers have been used to demonstrate the presence of myoepithelial cells in order to determine their role in the histogenesis of mammary tumors. p63, a recently characterized p53 homologue, is consistently expressed in myoepithelial cells of the human breast; however, no assessment of its immunoreactivity has been reported so far in canine mammary tissues. We investigated p63 immunohistochemical expression, as a novel myoepithelial cell nuclear marker, in 81 samples of normal (n = 2), hyperplastic (n = 11), and neoplastic (n = 68) canine mammary tissues. Myoepithelial phenotype was confirmed by using complementary monoclonal antibodies: alpha-smooth muscle actin, cytokeratin 14, cytokeratin AE1/AE3, and vimentin. p63 expression was observed in 91.4% (74/81) of the samples evaluated. Normal mammary glands, mammary hyperplasias, and benign tumors showed 100% immunoreactivity, with p63 expression restricted to myoepithelial cell nuclei. In general, benign mixed tumors showed a basal cell compartment immunoreactive to p63, with a gradual decrease of its expression during myoepithelial transformation. p63 expression was found in 72% of malignant tumors, allowing myoepithelial or basal cell identification in spindle-cell carcinomas (2/2), tubulopapillary carcinomas (8/9), solid carcinomas (7/10), and carcinosarcomas (1/3). The osteosarcoma analyzed was p63 negative. In our series, stromal components were consistently nonreactive to p63. In conclusion, the present study reveals p63 as a sensitive and highly specific marker of myoepithelial cells in canine mammary tissues, and the authors suggest p63 as an additional marker for defining myoepithelial histogenesis.     

Immunolocalization of the smooth muscle-specific protein calponin in complex and mixed tumors of the mammary gland of the dog: assessment of the morphogenetic role of the myoepithelium

The immunohistochemical expression of the smooth muscle-specific protein calponin was studied to assess the contribution of myoepithelial cells to the histogenesis of spindle cells of complex and mixed tumors of the mammary gland of the dog and the origin of cartilage and bone in mixed tumors. Formalin-fixed tissues from 55 benign and malignant tumors (49 also containing surrounding normal mammary gland) were evaluated. Periacinar and periductal myoepithelial cells of all the 49 normal mammary glands were diffusely stained by the anti-human calponin monoclonal antibody. Calponin was found in 53 (98%) of the tumors studied, reacting with the myoepithelium-like cells of 86% of benign tumors and their remnants in 85% of malignant tumors. Five different types of calponin-immunoreactive myoepithelial cells were identified: hypertrophic myoepithelial cells. fusiform cells, stellate myoepithelial cells, rounded (myoepithelial) cells, and chondroblasts. Differences in staining intensity and staining pattern among these five types of cells suggested a transition of myoepithelial cells to chondroblasts. Stromal myofibroblasts also showed calponin immunoreactivity, but they did not react with a cytokeratin 14 monoclonal antibody, which recognizes myoepithelial cells in mammary gland. Calponin appears to be a very sensitive marker of normal and neoplastic myoepithelium in the canine mammary gland, and its identification in different cell types of complex and mixed tumors of the mammary gland of the dog suggests a major histogenetic role for myoepithelial cells.     

Complex mammary carcinoma with metastases to lymph nodes,subcutaneous tissue,and multiple joints in a dog

An 8‐year‐old, intact female, mixed‐breed dog presented to the Oklahoma State University Boren Veterinary Medical Teaching Hospital for evaluation of progressive lameness and joint effusion of multiple joints. Physical examination revealed joint effusion of the elbow, hock, and stifle joints bilaterally, enlarged left axillary and right popliteal lymph nodes, a subcutaneous mass over the left elbow, and a subcutaneous mass involving the left second and third mammary glands. Cytologic examination of the mammary mass, enlarged lymph nodes, and joint fluid from most affected joints revealed a monomorphic population of loosely cohesive neoplastic epithelial cells. The patient was humanely euthanized, and subsequent necropsy with histopathologic examination revealed a complex mammary carcinoma with metastases to enlarged lymph nodes, subcutaneous tissue over the left elbow, and the synovium of multiple joints. Immunohistochemical stains were performed and showed diffusely positive pan cytokeratin, CK8/18, and CK19 staining in the neoplastic luminal epithelial cells of the mammary carcinoma, synovium, and lymph nodes, and showed diffusely positive vimentin staining of the myoepithelial cells. Myoepithelial calponin positivity was diffuse in the mammary mass and lymph nodes but minimal in the synovium. Only the mammary mass showed p63 positivity. Metastatic mammary neoplasia is relatively common in dogs; however, metastasis to the synovium has only been reported once previously in the literature. This is the first case utilizing immunohistochemistry for confirmation and characterization of metastases.     

Myoepitheliomas in inbred laboratory mice.

Myoepitheliomas are subcutaneous tumors that arise from myoepithelial cells of various exocrine glands. In a retrospective study of 142 tumors observed over a period of 3 years, myoepitheliomas occurred spontaneously in A/HeJ, A/J, BALB/cJ, BALB/cByJ, LLC.A/Ckc, and NOD/Lt inbred strains of mice. Tumors presented primarily in the subcutaneous tissues of the ventral neck (74% of the myoepitheliomas evaluated) but were observed in several other subcutaneous locations, including the head, perineum, and ventral abdomen. These areas were adjacent to salivary, mammary, clitoral, preputial, and Harderian glands. Forty myoepitheliomas were tested by the avidin-biotin complex technique with a panel of antisera specific for mouse keratins, intermediate filaments, and other cytoskeletal proteins to determine the cell type from which this neoplasm originated. Antibodies directed against the specific mouse keratins K5, K6, and K14, and a broadly cross-reactive cytokeratin antibody stained acinar and ductal myoepithelial cells in normal mammary, salivary, and Harderian glands, and neoplastic cells in all cases. Antisera directed against a smooth muscle actin (anti-alpha-sm-1) stained acinar myoepithelial cells of the glands and vascular smooth muscle but neither ductular myoepithelial cells nor tumor cells. This supports the notion that these tumors originate from extraglandular ductular myoepithelial cells. Southern blots, prepared from DNA extracted from nine myoepitheliomas, did not show restriction fragment length polymorphisms when mouse mammary tumor virus (MMTV) cDNA or Int-1 genomic DNA probes were used; this implies that a retrovirus is not the etiologic agent.     

Expression of class II beta-tubulin by proliferative myoepithelial cells in canine mammary mixed tumors

Benign mammary mixed tumors in dogs resemble human salivary pleomorphic adenomas with regard to their histogenesis, including the occurrence of cartilaginous or bony metaplasia as well as the expression pattern of cytoskeletal proteins in proliferative myoepithelial cells. Recently, a monoclonal antibody specific for class II beta-tubulin has been developed. The epitope it recognizes was determined to be the heptapeptide Glu-Glu-Glu-Glu-Gly-Glu-Asp, which is the common sequence found among the canine, rat, mouse, and human class II beta-tubulin-specific regions. We carried out immunohistochemical studies on mammary mixed tumors obtained from three female dogs using this the monoclonal antibody. The antibody to class II beta-tubulin reacted intensely with proliferative myoepithelial cells in canine mammary mixed tumors, whereas staining was barely detectable in normal myoepithelial cells surrounding alveoli and alveolar ducts within the tumor and adjacent normal tissue. Proliferative myoepithelial cells also expressed vimentin, but alpha-smooth muscle actin (alphaSMA) staining was barely detectable. Immunoblot analysis showed that class II beta-tubulin and vimentin were expressed in myoepithelial cell lines prepared from the three mammary mixed tumors. On the other hand, only one cell line, which was negative for alphaSMA, produced cartilage-specific type II collagen. These results suggest that class II beta-tubulin could be a new molecular marker of proliferating myoepithelial cells in canine mammary mixed tumors and that differential expression of cytoskeletal components is associated with cartilaginous metaplasia of proliferative myoepithelial cells in mixed mammary tumors.     

p53 gene mutations occurring in spontaneous benign and malignant mammary tumors of the dog

Sixty-three cases of benign and malignant canine mammary tumors were analyzed to define the alteration of exons 5-8 for the p53 tumor suppressor gene using polymerase chain reaction direct sequence analysis with paraffin-embedded tissues. Four missense mutations were found in 38 benign mammary tumors (11%), and five missense (one tumor had two missense mutations) and one nonsense mutations were found in 25 mammary carcinomas (20%). These data suggest that the p53 gene alterations might be initiated at an early stage of canine mammary carcinogenesis and p53 mutations might be associated with malignancy. However, there was no evidence of any relationship between the p53 alterations and the histologic types of tumors or breeds of dogs.     

Effect of spaying and timing of spaying on survival of dogs with mammary carcinoma

The risk of developing mammary gland tumors in dogs is significantly decreased by ovariohysterectomy at an early age. However, previous studies have not found a benefit to ovariohysterectomy concurrent with tumor removal in dogs with established mammary gland tumors, suggesting that the progression of these tumors is independent of continued estrogen stimulation. The purpose of this study was to evaluate the effect of spaying and of the timing of spaying on survival in dogs with mammary gland carcinoma. Signalment, spay status and spay age, tumor characteristics, treatment. survival, and cause of death of 137 dogs with mammary gland carcinoma were analyzed. The dogs were classified into 3 groups according to spay status and spay time: intact dogs, dogs spayed less than 2 years before tumor surgery (SPAY 1), and dogs spayed more than 2 years before their tumor surgery (SPAY 2). Dogs in the SPAY 1 group lived significantly longer than dogs in SPAY 2 and intact dogs (median survival of 755 days, versus 301 and 286 days, respectively, P = .02 and .03). After adjusting for differences between the spay groups with regard to age, histologic differentiation, and vascular invasion, SPAY 1 dogs survived 45% longer compared to dogs that were either intact or in the SPAY 2 group (RR = .55; 95% CI .32-.93; P = .03). This study reveals ovariohysterectomy to be an effective adjunct to tumor removal in dogs with mammary gland carcinoma and that the timing of ovariohysterectomy is important in influencing survival.     

Expression of bone morphogenetic protein-6 (BMP-6) in myoepithelial cells in canine mammary gland tumors.

Seventy-three mammary tumors and three mammary tissue specimens were examined to elucidate the expression of bone morphogenetic protein (BMP)-6 in the myoepithelial cells of canine mammary gland tumors. Morphologically, the myoepithelial cells were classified into four types: resting and proliferating cells inside the basement membrane, and spindle- and star-shaped cells proliferating in the outer area of the basement membrane. The characteristics of these myoepithelial cells were confirmed by immunohistochemistry using antibodies raised against keratin, cytokeratin 19, alpha-smooth muscle actin, and vimentin. In simple adenoma, a small number of resting myoepithelial cells was immunopositive for BMP-6. In complex adenomas and benign mixed tumors, all types of myoepithelial cells, depending in some cases on their specific location within the tumor, were immunopositive for BMP-6, but almost all of the tubular epithelial cells were immunonegative. Foci consisting of a proliferation of BMP-6-positive star- and spindle-shaped cells had mucinous stroma with marked hyaline and chondroid changes. In contrast, the foci with BMP-6-negative spindle- and star-shaped cells tended to have mucinous stroma without chondroid change. Several types of mesenchymal cells including chondrocytes, osteoblasts, and fibroblastlike cells in the mixed tumors, showed an intense immunopositive reaction for the BMP-6 antibody, and were located close to the ectopic cartilage and bone matrix. No significant immunoreactivity for BMP-6 was observed in most of the malignant mammary tumors; only one malignant mixed tumor was examined. All of these findings indicate that BMP-6 expression in myoepithelial cells may increase in complex adenomas and benign mixed tumors in canine mammary glands, and that BMP-6 expression is most intense in the vicinity of chondroid matrix in these tumors.     

GH-producing mammary tumors in two dogs with acromegaly

Two intact female dogs were admitted for growing mammary tumors. They had symptoms of acromegaly including weight gain, enlargement of the head, excessive skin folds, and inspiratory stridor. Serum concentrations of growth hormone (GH), insulin-like growth factor-I (IGF-I), and insulin were elevated in the two cases. From these findings, both dogs were diagnosed with acromegaly. In case 1, the GH, IGF-I, and insulin levels subsided after removal of the focal benign mammary tumors and ovariohysterectomy. In case 2, those levels subsided after removal of only focal mammary carcinoma. In both cases, immunohistochemical investigations for GH were positive in the mammary tumor cells but not in the normal mammary glands. We concluded that GH-producing mammary tumors caused the present acromegaly.     

Inflammatory mammary carcinoma in dogs: 33 cases (1995-1999).

OBJECTIVE: To determine epidemiologic, clinical, and pathologic characteristics of inflammatory mammary carcinoma (IC) in dogs. DESIGN: Retrospective study. ANIMALS: 33 dogs with IC and 153 dogs with malignant mammary tumors other than IC. PROCEDURES: Medical records were reviewed, and signalment, history, physical examination findings, and results of thoracic radiography and necropsy were obtained. RESULTS: 33 of 436 (7.6%) dogs examined at a veterinary teaching hospital because of dysplasia or tumors of the mammary glands and 33 of 186 (17.7%) dogs with at least 1 malignant tumor had IC. Thirty-two of the 33 dogs were sexually intact. Dogs with IC were significantly older than were dogs with other malignant mammary tumors, and in dogs with IC, the tumor was initially noticed a mean of 52 days after the beginning of the last observed estrus, whereas in dogs with other mammary tumors, the tumor was initially noticed a mean of 137 days after the beginning of the last observed estrus. Dogs with IC were more likely to be anorectic and to have generalized weakness, weight loss, and thoracic metastases. Dogs with IC survived a mean of 25 days with palliative treatment. Histologically, involvement of dermal lymphatic vessels was identified in 14 of 19 (74%) dogs with IC. Two clinical forms of IC (primary and secondary) were identified. Dogs with primary IC had a worse clinical condition. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that IC is an uncommon but distinct entity in dogs. A histologic finding of dermal lymphatic involvement should be considered a hallmark for the pathologic diagnosis of IC in dogs.     

Immunohistochemical analysis of cyclin A, cyclin D1 and P53 in mammary tumors, squamous cell carcinomas and basal cell tumors of dogs and cats

The involvement of cyclin A, cyclin D1 and p53 proteins in canine and feline tumorigenesis was analyzed immunohistochemically. In the present study, a total of 176 cases were examined, among which there were 108 canine cases (75 mammary lesions, 16 squamous cell carcinomas and 17 basal cell tumors) and 68 feline cases (43 mammary lesions, 20 squamous cell carcinomas and 5 basal cell tumors). Speckled nuclear staining for cyclin A was observed in 19/38 (50%) canine malignant mammary tumors and 18/37 (48.6%) feline mammary carcinomas, while this was not seen in benign mammary tumors of either dogs or cats. Marked intense nuclear cyclin A staining was seen in 7/16 (43.8%) canine squamous cell carcinomas and 18/20 (90.0%) feline squamous cell carcinomas. Only 3/17 (17.6%) canine basal cell tumors showed slight and scattered staining for cyclin A. Expression of cyclin D1 was very rare in both canine and feline tumors. Nuclear staining of p53 was found in 7/37 (18.9%) feline mammary carcinomas. Intense immunoreactivity for p53 was found in 6/16 (37.5%) canine squamous cell carcinomas and 8/20 (40%) feline squamous cell carcinomas. These results suggest that cyclin A may have a role in the proliferation of canine malignant mammary tumors, feline mammary carcinomas and squamous cell carcinomas of dogs and cats, and p53 may associate with the tumorigenesis of feline mammary carcinomas and squamous cell carcinomas of dogs and cats.     

犬常见肿瘤流行病学调查及组织病理学诊断

为探讨犬常见肿瘤的发病规律，试验收集哈尔滨地区2016-2017年宠物医院部分犬肿瘤病例71例，采用组织病理学方法对犬肿瘤进行病理学诊断，并对患病动物的品种、性别、年龄、发生部位和饮食情况与肿瘤发生关系进行统计分析。结果显示，71例确诊肿瘤病例中，恶性肿瘤28例，包括鳞状上皮细胞癌3例，基底细胞癌5例，乳腺癌14例，淋巴瘤2例，肾母细胞瘤、精原细胞癌、生殖细胞癌、侵袭性血管黏液瘤各1例；良性肿瘤43例，包括良性乳腺肿瘤15例，纤维瘤10例，平滑肌瘤5例，乳头状瘤和精原细胞瘤各3例，造釉细胞瘤、耵聍腺瘤、脂肪瘤、结节样增生、性索间质细胞瘤、颗粒细胞瘤、肛周腺瘤各1例。上述病例中，乳腺和皮肤是犬肿瘤的高发部位，分别占全部患犬的40.8%和34.0%；患病犬年龄1~16岁不等，平均发病年龄为9.1岁，7岁以后是肿瘤的高发期，中老年犬仍为主要发病群体，但低龄犬发病数量上升；各品种犬均可发生肿瘤，其中杂种犬发病率最高，其次是贵宾犬和京巴犬，且主要为乳腺肿瘤；饮食习惯主要以剩饭剩菜类和肉拌饭类为主，分别占患犬总数的39%和30%；部分肿瘤类型与犬的性别、是否绝育有关，如乳腺肿瘤多发生于未绝育的老年母犬。本研究结果为犬肿瘤的流行病学及诊断提供了参考依据，对犬肿瘤的预防和诊断有一定的借鉴意义。     

The expression of intermediate filaments in canine mammary glands and their tumors

Monoclonal antibodies specific for different types of intermediate filaments (cytokeratin, vimentin, desmin and neurofilaments) were used to study the histogenesis of canine mammary glands and 57 canine mammary tumors by immunocytochemistry. The intra- and interlobular duct epithelium, acinar, and intralobular myoepithelial cells stained positively for cytokeratin. Peripheral ductal and acinar cells, as well as interstitial cells, stained positively for vimentin. A similar staining pattern was seen in adenomas, complex adenomas, benign mixed tumors, ductular carcinomas, and one myoepithelioma-like tumor. Additionally, cytokeratin positive cells were scattered interstitially in one single adenoma, most complex adenomas, some benign mixed tumors, complex carcinomas, and in the malignant mixed tumors. All stromal cells stained positively for vimentin. The fibrosarcomas were positive only for vimentin, while the following expressed both desmin and cytokeratin: epithelial-like cells in one adenoma, three complex adenomas, the myoepithelioma-like tumor, the single comedo carcinoma, two complex carcinomas, the single lobular carcinoma, one malignant mixed tumor, and three osteosarcomas. Epithelial-like cells in one adenoma, six complex adenomas, two benign mixed tumors, two complex carcinomas, the lobular carcinoma, and the malignant schwannoma stained for neurofilaments. Three tumors, one adenoma, one complex adenoma, and the lobular carcinoma expressed both desmin and neurofilaments in addition to cytokeratin and vimentin. The results show the expression of different types of intermediate filaments and indicate that there might be a stem cell origin in most of the canine mammary tumors.     

A Spontaneous Epithelial-Myoepithelial Carcinoma of the Submandibular Gland in a Sprague-Dawley Rat

The present report describes a rare case of spontaneous tumor of the salivary gland in a male Sprague-Dawley rat. The clinically confirmed mass rapidly developed in the cervical region between 19 and 21 weeks of age, and the animal was subsequently euthanized. At necropsy, a well-circumscribed nodule approximately 7 × 6 cm in diameter was found at the site of the salivary gland. The cut surface of the nodule was lobulated and soft and had a pinkish tan fish-flesh appearance. One large cyst (approximately 3 × 2 cm in size) containing reddish fluid was also present in the nodule. Histopathologically, the tumor, with a partially lobulated structure, was surrounded by a thin fibrous capsule. The majority of tumor cells formed a diffuse solid sheet structure that mainly consisted of small ovoid or spindle-shaped cells. In the tumor periphery, some cells were arranged in nest-like structures. Small duct-like structures lined with a monolayer of cuboidal epithelial cells resembling an intercalated duct or large polygonal clear cells with a myoepithelial component were also observed. Mitotic figures and necrotic foci were frequently observed in solid areas. Immunohistochemically, the tumor cells were positive for cytokeratin, epithelial membrane antigen, vimentin, p63, α-smooth muscle actin and calponin. The cells were negative for calcitonin, synaptophysin and chromogranin A. On the basis of these findings, the tumor was diagnosed as an epithelial-myoepithelial carcinoma originating from the luminal epithelial cells and myoepithelial cells in the submandibular gland.     

Calponin expression and myoepithelial cell differentiation in canine, feline and human mammary simple carcinomas

Calponin is a 34‐kDa smooth muscle‐specific protein that has been shown to be a highly sensitive marker of myoepithelial cells in canine, feline and human mammary tissue and tumours. The expression of calponin was studied in 15 canine, 32 feline and 28 human simple mammary carcinomas using a monoclonal mouse antihuman calponin antibody and the avidin–biotin peroxidase complex (ABC) immunohistochemical technique. Calponin expression was compared with the expression of cytokeratin 14, a marker of normal mammary myoepithelial cells in the three species. Four different types of calponin‐positive cells were identified: (1) Type 1: cytokeratin‐14‐positive pre‐existing myoepithelial cells forming a continuous layer with images of focal disruptions; (2) Type 2: cytokeratin‐14‐positive isolated nests of fusiform, polygonal or round cells without atypia; (3) Type 3: cytokeratin‐14‐positive atypical cells indistinguishable from non‐reactive atypical cells, which should have never been detected in haematoxylin and eosin‐stained sections and (4) Type 4: cytokeratin‐14‐negative stromal fusiform cells around the neoplastic growth or cell nests, identified as myofibroblasts. Calponin‐negative and cytokeratin‐14‐positive atypical neoplastic cells were observed in three canine, 28 feline and two human carcinomas. The latter were indicative of altered expression of high‐molecular‐weight cytokeratins in luminal epithelial‐type simple carcinomas. Our findings show that calponin is a good marker of myoepithelial cell differentiation in feline, human and, particularly, canine simple carcinomas. The high number (six out of 15) of canine tumours with type 3 cells points to the need of both introducing calponin examination in the routine diagnostic schedule and performing further studies on its prognostic significance.     

Canine cutaneous clear cell adnexal carcinoma: histopathology, immunohistochemistry, and biologic behavior of 26 cases.

Thirty tumors including 27 distinctive cutaneous neoplasms and 3 metastatic tumors from 26 dogs were collected from diagnostic submissions to 3 laboratories. Characteristic histopathologic features included location in the subcutis or dermis (or both); lobular, nodular, and nest-like architecture; and a component of epithelioid cells with clear cytoplasm. Additional features present in most cases included follicular dermal papilla-like structures, low mitotic index, nuclear pleomorphism, necrosis, and mineralization. Cytoplasmic periodic acid Schiff-positivity, which was abolished by pretreatment with diastase, indicated the presence of glycogen in all cases. The oil red O stain did not demonstrate cytoplasmic lipid. Melanin granules, accentuated by the Fontana-Masson method, were observed infrequently. A sparsely cellular mucinous stroma and stromal cartilaginous differentiation were uncommon. By immunohistochemistry, neoplastic cells stained positively for cytokeratin (29 of 29), vimentin (28 of 28), S-100 protein (24 of 29), and melan A (8 of 12); results were negative for smooth muscle actin and calponin in all cases. Clinical follow-up information was obtained on all 26 dogs. One tumor recurred, 1 metastasized to a regional lymph node, and 1 metastasized to regional lymph nodes twice. In another case, possible pulmonary metastasis was noted radiographically. The findings are consistent with a poorly differentiated, low-grade, adnexal carcinoma of the skin. Similar canine cutaneous neoplasms have been reported as "clear-cell hidradenocarcinoma" and "follicular stem cell carcinoma." The authors propose the designation "cutaneous clear cell adnexal carcinoma."     

Co-localization of chondromodulin-I (ChM-I) and bone morphogenetic protein-6 (BMP-6) in myoepithelial cells of canine mammary tumors

To compare the roles of chondromodulin-I (ChM-I) and bone morphogenetic protein-6 (BMP-6) in ectopic mesenchymal tissue formation in canine mammary gland tumors, 33 tumors and 2 normal mammary glands were examined. Immunohistochemical analysis revealed co-expression of ChM-I and BMP-6 in canine mammary tumors. In mixed tumors, newly formed woven bone with ossified cartilage matrix was observed in 4/9 cases. The osteoblasts lining the woven bone showed moderate immunoreactivity to ChM-I and BMP-6. Almost all chondrocytes and proliferative myoepithelial cells within the basement membrane showed intense immunoreactivity to both, and the myoepithelial cells adjacent to the mature cartilage showed the most intense immunoreactivity. The immunoreactivity to ChM-I and BMP-6 of the interstitial myoepithelial cells in the myxomatous stroma varied in each focus of mixed tumors. Similar findings were found in complex adenomas. In simple adenomas, hyperplasic myoepithelial cells within the basement membrane showed moderate immunoreactivity to both markers. Western blot analysis detected a 25 kDa band of ChM-I in fresh tissue samples from three mixed tumors. Our results support the hypothesis that proliferating myoepithelial cells with ChM-I and BMP-6 expression play important roles in mesenchymal metaplasia in canine mammary tumors.