Medullary Thyroid Carcinoma in a Maltese Dog

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pISSN 1598-298X

J Vet Clin 31(5) :435-₄₃₈ (2014)

435

Medullary Thyroid Carcinoma in a Maltese Dog

Hee-Jin Hyun, Soo-Kyo Jung and Jae-Hoon Kim¹

College of Veterinary Medicine and Veterinary Medical Research Institute, Jeju National University, Jeju 690-756, Korea (Accepted: October 7, 2014)

Abstract : An 11-year-old, 2.67 kg female Maltese dog with 3 weeks history of palpable cervical mass near trachea was submitted to a local animal hospital. Radiography and ultrasonography showed radiopaque mass adjacent trachea and vagus nerve. Surgically excised mass was solitary and approximately 3.5× 2 × 0.8 cm in size. Histopathologically, there were large neoplastic foci admixed with normal thyroid tissues. These neoplastic foci were composed of small to large packets of the neoplastic cells with plasmacytic morphology, and these packets were divided by fine fibrovascular septa. Immunohistochemically, most neoplastic cells in the thyroid mass showed positive reactions for cytokeratin (AE1/AE3), chromogranin A, neuron specific enolase (NSE) and the negative reaction for vimentin. Based on the gross, histopathologic and immunohistochemical characteristics, this dog was diagnosed as medullary thyroid carcinoma.

Key words : chromogranin A, dog, immunohistochemistry, medullary thyroid carcinoma, NSE.

Introduction

Thyroid nodules are frequently observed in humans, partic- ularly women, and most are benign (1). Thyroid nodules are relatively common in older cats, but rare in the dog. Tumors of the thyroid gland account for only 1.2 to 3.8% of reported neoplasia in dogs (8). Yet, they are the most common form of endocrine neoplasia in dogs. Malignant thyroid tumors are more common than benign tumors and account for 63 to 87%

of all thyroid masses (3). Adenomas are not commonly de- tected clinically, and are incidental findings at necropsy (1,3).

Malignant thyroid tumors can arise from either follicular or parafollicular cell lineages. Follicular thyroid carcinomas are more common in dogs (1). Parafollicular carcinomas, also known as medullary or C-cell carcinomas, are considered rare, accounting for varies widely from 1.4% to 36%, respectively (2,3). Contrary to human tumors, canine medullary thyroid carcinoma is usually more encapsulated and less invasive than thyroid adenocarcinoma and carries a more favorable prognosis (3). However medullary thyroid carcinoma in animals has been rarely reported in Korea. Thus, more detailed description of this neoplasm in dogs may be needed. Here we report a case of gross, histopathologic and immunohistochemical features of medullary thyroid carcinoma in a dog.

Case

An 11-year-old, 2.67 kg female Maltese dog with 3 weeks history of palpable cervical mass near trachea was submitted to a local animal hospital. Complete blood count (CBC) and

serum chemistry profiles were performed. Results of blood works were within normal ranges. Abnormalities in serum chemistry profile included decreased in GOT (10 U/L; reference range, 16-50) and albumin (2.9 g/dL; reference range, 3.1-4.1). Serum T4 level in dog was mild decreased (1.1 ug/

dL; reference range, 1.6-5). Radiography and ultrasonography showed radiopaque mass adjacent trachea and vagus nerve. The cervical mass was surgically excised, and no complications were observed after surgery. Thirty two months later the owner described the dog in good health and normal condition. There had been no recurrence of the cervical swelling to date.

Surgically excised mass was immediately fixed in 10%

neutral buffered formalin, and then referred to the Pathology Department of Veterinary Medicine, Jeju National Univer- sity. Grossly, the mass was solitary and approximately 3.5

× 2 × 0.8 cm in size. On the cut surface, the mass showed white to tan color and surrounded by thin connective tissues.

Several small white necrotic foci about 0.5× 0.3 cm in size were observed in the center of the mass (Fig 1). The sample was embedded in paraffin, sectioned at 3µm and stained with hematoxylin and eosin (H&E). Immunohistochemical (IHC) staining was performed to clarify the origin of neoplastic cells using antibodies for cytokeratin (AE1/AE3), chromogranin A, neuron specific enolase (NSE), and vimentin. The antibody type, working dilution, and source for each antibody were listed in Table 1.

On histopathologic examination, there were extensive hyperplasia of parafollicular cells and the neoplastic foci admixed with normal thyroid tissues (Fig 2). These neoplastic foci were composed of small to large packets of the neoplastic cells, and these packets were divided by fine fibrovascular septa (Fig 3). The neoplastic cells were round to oval shape with oval to mild spindle nuclei and have an abundant eosinophilic granular cytoplasm. Many neoplastic

1Corresponding author.

E-mail: [email protected]

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436 Hei-Jin Hyun, Soo-Kyo Jung and Jae-Hoon Kim

cells exhibited a plasmacytic morphology characterized by abundant cytoplasm and an eccentrically located nucleus.

The cellular margin was indistinct, and multifocally scattered lymphocytes and hemorrhage were also presented in the mass. Multifocal necrotic foci also scattered in the mass.

These neoplastic cells showed invasive tendency to adjacent connective tissues and capsule (Fig 3), therefore small nests of neoplastic cells were formed. According to IHC staining, most neoplastic cells in the thyroid mass showed strong pos-

itive reactions for AE1/AE3 (Fig 4A), an epithelial cell marker, chromogranin A (Fig 4B), a neuroendocrine cell marker, and NSE (Fig 4C), a neuronal and neuroendocrine cell marker. However there were negative reactions for vimentin (Fig 4D), a mesenchymal cell marker. The histopathologic and immunohistochemical features of the neoplasm were consistent with medullary thyroid carcinoma.

Discussion

Medullary thyroid carcinoma is a neoplasm that arises from the calcitonin producing C cells of the thyroid gland (10). The C cells were first identified in 1876 in the thyroid glands of the dog. After that one researcher demonstrated calcitonin production in these cells and called them C cells, and included them in the amine-precursor-uptake and decar- boxylation (APUD) system, thus proposing a neuroectoder- mal origin for the cells (12). The original APUD concept has been modified to the diffuse neuroendocrine system concept to include the endodermal differentiation in some canine medullary thyroid carcinoma using immunohistochemical study (10).

Fig 1. The cervical mass from a maltese dog. Note well-encapsulated mass with white necrotic foci in the center of mass.

Table 1. Type, dilution, and source of antibodies in immunohistochemical staining

Antibody Type / Clone Dilution Source Cytokeratin Monoclonal mouse

AE1/AE3 1:50 DAKO

Chromogranin A Polyclonal rabbit 1:100 DAKO NSE Monoclonal mouse

BBS/NC/VI-H14 1:100 DAKO Vimentin Monoclonal mouse

V9 1:100 DAKO

Fig 2. Extensive hyperplastic c-cells and neoplastic foci were admixed with normal thyroid tissues in right side. H&E, Bar

= 100µm.

Fig 3. Neoplastic foci were composed of small to large packets of plasmacytic cells, and these packets were divided by fine fibro-vascular septa. Note invasion (arrow) to adjacent tissues.

H&E, Bar = 200µm.

Fig 4. Note strong positive immunoreactivity for AE1/AE3 (A), chromogranin A (B) and NSE (C), and negative reaction for vimentin (D). IHC, Bar = 20µm.

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Medullary Thyroid Carcinoma in a Maltese Dog ₄₃₇

Although there have been applied so many diagnostic tech- niques, diagnosis of thyroid tumors are best achieved through histologic examination of a biopsy sample with or without cytology (1). The major types of thyroid carcinomas are follicular, papillary, compact cellular (solid), undifferentiated thyroid carcinoma, and malignant mixed thyroid tumors. In dogs with thyroid carcinoma, both a follicular and compact cellular growth pattern are more frequently encountered, whereas papillary carcinomas are rare (9). The microscopic features of medullary thyroid carcinoma are distinct from thyroid carcinomas (10). The most common growth pattern and typical features are solid with sheets or nests of medium- sized neoplastic cells separated by fine fibrovascular stroma (9,10). The hallmark of malignancy in thyroid tumors that distinguishes them from benign tumors is the presence of capsular or vascular invasion (1). Many small nests of neoplastic cells due to invasion were presented at the surround- ing connective tissues and the capsule in this thyroid mass.

The overall histopathoilogic findings in this case was very similar those of previous reports. However, amyloid that has been reported to be a common finding in human and frequently in animals (9,10,13), was not noted in this case.

Because of similar histopathologic appearance, it is diffi- cult to distinguish medullary thyroid carcinoma from compact cellular thyroid carcinoma with routine microscopic examination alone (1,3). Immunohistochemistry is considered essential for distinguishing between these tumors (3,10). Sev- eral immunohistochemial studies for the medullary thyroid carcinomas using NSE, chromogranin A, calcitonin, cytokeratin, and vimentin have been performed to dogs and other animal cases (2,4,5,10,13). According to previous literature, the diagnosis of medullary thyroid carcinoma was estab- lished on the basis of histological and immunocytochemical criteria using sixteen dogs (10). They suggested that several markers such as calcitonin (16/16, 100%), NSE (14/16, 88%), cytokeratin AE1/AE3 (13/16, 81%), and synaptophysin (11/

16, 69%) can be used to confirm the diagnosis of medullary thyroid carcinoma in dogs. Recently, it is suggested that thy- roglobulin and calcitonin are the two most useful markers for differentiating thyroid follicular tumors or medullary thyroid tumors in dog, respectively (2,13).

NSE is an isomer of the glycolic enolase found in neurons and neuroendocrine cells including C cells in thyroid (14).

However, tumors of follicular cell origin are not reported to be positive for NSE in human (7). Chromogranin A was first isolated from secretory granules of the bovine adrenal medulla and is a major constituent of secretory granules of the adrenal medulla, pituitary, parathyroid, thyroid C cells, pancreatic islets, endocrine cells of the gastrointestinal tract, and sympathetic nerve (6). Antibodies to chromogranin A have proven to be excellent broad spectrum markers for cells of the dispersed neuroendocrine system and their tumors (4,6). Medullary thyroid carcinoma is positive for chromogranin A and calcitonin, whereas thyroid follicular cell carcinoma is negative for these markers (4,10). Only one case out of 16 canine medullary thyroid carcinomas was reacted with vimentin (10). In this case, the thyroid neoplasm showed positive reactions for AE1/AE3, chromogranin A, NSE, and negative reactions for vimentin. Therefore tumor mass in thy-

roid gland was diagnosed as a medullary thyroid carcinoma on the basis of histological and immunohistochemical characteristics.

Parathyroid adenocarcinoma may be associated with hyper- calcemia (2). Although hypocalcemia has been reported in some dogs with medullary thyroid carcinoma (11), the dog in this study had normal serum calcium status as previously described (2,3). Thyroid carcinomas often grow rapidly and invade adjacent organs such as the lung, trachea, esophagus, and larynx (9). However, medullary thyroid carcinoma metastases in dogs have been limited to the regional lymph node, with the exception of previous case in which distant metastases have been reported (5). Neither metastasis nor recurrence was observed in this study. In addition, this dog continued normal healthy life for 32 months after surgical excision of cervical mass.

In summary, this case report described the clinical, histological, and immunohistochemical characteristics of medullary thyroid carcinoma in dog. Immunohistochemical staining against NSE, chromogranin A, and AE1/AE3 combination might be useful markers for medullary thyroid carcinoma in dogs when calcitonin was not available.

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말티즈 개에서 발생한 갑상선수질암

현희진·정수교·김재훈¹

제주대학교 수의과대학, 수의과학연구소

요 약 : 11세령, 체중 2.67 kg, 암컷 Maltese의 기관 인근 경부에서 3주 전부터 종괴가 촉진되어 동물병원에 내원하였 으며, 방사선 및 초음파 검사 결과 기관 및 미주신경 주위에 불투과성의 종괴가 확인되었다. 외과적으로 절제된 단일 한 종괴의 크기는 3.5 × 2 × 0.8 cm였다. 병리조직학적으로 큰 종양 병소가 정상 갑상선 조직과 혼재되어 있었다. 종양 병소는 형질세포와 같은 형태를 보이는 종양세포들이 모여 있는 다양한 크기의 소포로 구성되어 있고, 이 소포들은 미 세한 섬유혈관중격에 의해 구획되어 있었다. 종양세포들은 인근 결합조직과 피막으로 침습하는 경향을 나타내었다. 면 역조직화학염색을 실시한 결과 종양세포들은 사이토케라틴(AE1/AE3), 크로모그래닌 A, 신경원 특이 에놀라제(NSE)에 대하여 강한 양성 반응을, vimentin에는 음성 반응을 보이고 있었다. 육안병변, 병리조직학적 및 면역조직화학 염색의 특징을 토대로 본 증례는 갑상선수질암으로 진단되었다.

주요어 : 크로모그래닌 A, 개, 면역조직화학염색, 갑상선수질암, 신경원 특이 에놀라제