Korean Journal of
Veterinary Service

A chondrosarcoma is a malignant neoplasm in which tumor cells produce varying amount of neoplastic chondroid and fibrillar matrix (Thompson and Dittmer, 2017). The tumor cells in chondrosarcoma never produced osteoid, but bone tissue may develop by metaplasia or by endochondral ossification (Thompson and Dittmer, 2017). Chondrosarcomas are classified as skeletal or extraskeletal (Munday and Prahl, 2002). Most chondrosarcomas develop from the skeletal cartilage, but extraskeletal chondrosarcomas occur in the soft tissue or parenchymal organs where no cartilage basically existed (Chikata et al, 2006; Thompson and Dittmer, 2017). Extraskeletal chondrosarcomas are rare tumors in both humans and animals (Patnaik, 1990; Casadei et al, 1991). In the canine population, approximately 1% of chondrosarcomas develop in an extraskeletal location (Patnaik, 1990; Munday and Prahl, 2002). Canine extraskeletal chondrosarcomas occurred in the larynx (Flanders et al, 1987), lungs (Patnaik, 1990), pericardium (LaRock et al, 1997), atrium (Southerland et al, 1993; Albers et al, 1997), mitral valve (Patnaik 1990), aorta (Anderson et al, 1988), omentum (Patnaik, 1990), retroperitoneum (Munday and Prahl, 2002), liver (Chikata et al, 2006), and spleen (Miller et al, 2005). Histologically, 2 different types of chondrosarcoma are recognized: myxoid, the most common type found in skeletal tumors, and mesenchymal, the rarer type found more often in extraskeletal sites (Casadei et al, 1991). So far, some cases of mesenchymal chondrosarcoma were reported in the dog and cat (Patnaik, 1990; Southerland et al, 1993; Albers et al, 1997; LaRock et al, 1997; Madarame et al, 1998; Rhind and Welsh, 1999; Munday and Prahl, 2002; Miller et al, 2005; Romanucci et al, 2005). Recently a rarer case of mesenchymal chondrosarcoma in the maxillary gingiva of Maltese dog was reported in Korea (Yim et al, 2021). This report described a case of extraskeletal mesenchymal chondrosarcoma originated from the spleen in a dog.

A seven-year-old, male Yorkshire Terrier dog weighing 3.3 kg was referred to the local animal hospital with a history of weight loss, anorexia and abdominal distension. Physical examination, complete blood count (CBC), serum chemistry profile, and abdominal radiographs (lateral and ventrodorsal view) were performed. A CBC revealed severe leukocytosis with lymphocytosis, neutropenia and eosinophilia (Table 1). Mild anemia and dehydration with erythrocytopenia were also presented (Table 1). Serum chemistry profile was normal range except for a decrease in BUN (Table 1).

Table 1 . Complete blood count and serum chemistry in a Yorkshire Terrier dog with a splenic mass.

Parameters	Data	Reference range
WBCs (103/μL)	49.29	6.0∼17.0
Lymphocytes (%)	45.7	10.0∼40.0
Neutrophils (%)	23.3	50.0∼80.0
Eosinophils (%)	21.5	1.6∼7.5
Hematocrit (%)	29.7	35.0∼55.0
RBCs (106/μL)	5.03	5.5∼8.5
BUN (mg/dL)	4.0	6.8∼29.6

BUN, blood urea nitrogen..

Survey abdominal radiographs showed an unclear intraabdominal organ silhouette without any abnormalities in the bony structures of the body (Fig. 1). An enlarged soft tissue mass in the spleen was noted in radiological findings, and then total splenectomy was performed. During the surgery, multiple adhesions between the splenic mass and intestine were also observed. According to the telephone call from veterinarian in animal hospital, the dog had a weight loss about 0.6 kg and died on the third day after the surgical operation.

Figure 1. Lateral view of radiography revealed increased soft-tissue opacity of the splenic mass in the abdomen (arrows).

The completely excised splenic mass was fixed in 10% buffered formalin and submitted to the pathology laboratory at the College of Veterinary Medicine in Jeju National University. The mass was trimmed, processed routinely, embedded in paraffin wax, and sectioned at 2∼3 ^mm. Deparaffinized sections were stained with hematoxylin and eosin (H&E), Masson’s trichrome, and alcian blue (pH 1.0 and 2.5) for light microscopic examination. Additional sections were available for immunohistochemistry (IHC). After mounting on the silane coated slide glasses, each section was performed with a labeled streptavidin-biotin method. To determine the origin of the tumor cells and the presence of chondrocytes, paraffin sections of the splenic mass were subjected to immunohistochemical analysis and incubated with following primary antibodies: mesenchymal markers, anti-vimentin (1:100, mouse monoclonal, DAKO, Denmark) and cartilaginous markers, anti-S-100 (1:400, rabbit polyclonal, DAKO, Denmark) were used. According to manufacturer information, these two antibodies display a cytoplasmic staining pattern.

Grossly, a large protruded splenic mass (approximately 13×10×8 cm in size, 405 g) which had relatively distinct border, soft to moderately firm and multilobulated (Fig. 2). On the cut surface, the mass was off-white to tan, dark red, and rust colored with many cavitation and had glossy and gelatinous area.

Figure 2. Note the multilobulated, firm, large protruded splenic mass (approximately 13×10×8 cm in size).

Histologically, the mass was well demarcated by vascularized fibrous bands. The tumor cells were characterized by coexistence of the primitive mesenchymal tissues and mature or immature cartilage tissues (Fig. 3A and 3B). Primitive mesenchyme was composed of round/oval tumor cells arranged in sheets or spindle shaped immature tumor cells and separated by fibrovascular stroma. These tumor cells had scant pale eosinophilic cytoplasm and indistinct cellular borders. The tumor cells showed marked anisocytosis and 1 to 4 mitotic figures per high power field (Fig. 3C). Occasionally bi- or multi-nucleated tumor cells also observed in most pleomorphic area. Tumor stromas had variable amounts of pale stained or vacuolated matrix. In some areas of the primitive mesenchymal region, many blood vessels were compressed or elongated by surrounding condensed mesenchymal tumor cells. Cartilage areas were scattered throughout the lesions: tumor cells were located in basophilic or eosinophilic extracellular cartilaginous matrix and had vacuolated cytoplasm, round vesicular nuclei and few mitotic figures. Neoplastic chondrocytes located in the lacunae showed markedly anisocytosis and anisokaryosis (Fig. 3D). Severe multifocal hemorrhage, necrosis, and fibrin deposition with mineralization also presented throughout the mass. Variably sized necrotic area contained a large number of dying cells, cellular debris and neutrophils. Numerous hemosiderin laden macrophages and some megakaryocytes were also present in the normal splenic parenchyma area, adjacent of the mass. In additional special stains, intercellular chondroid matrix was stained blue with Masson’s trichrome (Fig. 3B) and deep blue with alcian blue (both pH 1.0 and 2.5, Fig. 3B insert), respectively. Immunohistochemically, most of the tumor cells in splenic mass, cartilage and mesenchyme areas, demonstrated strong cytoplasmic immunoreactivity with the antibody against vimentin, a tumor marker to identify mesenchyme origin (Fig. 4A). And approximately 40% of the cells, especially in chondroid foci, demonstrated strong cytoplasmic and nuclear immunoreactivity with the antibody against S-100, a marker to confirm chondrocytes (Fig. 4B).

Figure 3. Histopathologic characteristics of tumor cells. (A) Note coexistence of primitive mesenchyme and mature or immature cartilages (arrow). H&E, ×100. (B) The intercellular chondroid matrix was stained blue, but primitive mesenchyme was red in color. Masson’s trichrome, ×100. (B, insert) Neoplastic cartilaginous cells were stained blue. Alcian blue, ×400. (C) Mesenchymal tumor cells are round/oval or spindle cells with high mitotic figures (arrows). H&E, ×400. (D) Neoplastic chondrocytes located in the lacunae showed marked anisocytosis and anisokaryosis. H&E, ×400.

Figure 4. (A) Neoplastic mesenchymal cells and cartilaginous cells demonstrated strong positive reaction for vimentin, whereas some neoplastic chondrocytes were positive for S-100 (arrow, B). IHC, ×100. (B, insert) Neoplastic cartilaginous cells were positive for S-100. IHC, ×200.

Based on the gross findings, histopathology and immunohistochemistry, this splenic mass was diagnosed as extraskeletal mesenchymal chondrosarcoma in a Yorkshire Terrier dog. Since there was no historical, physical, and radiographic evidence of skeletal involvement of neoplasm, the spleen was the primary site of this tumor.

Mesenchymal chondrosarcoma, a distinct variant of chondrosarcoma, in dogs were first diagnosed and recognized in 1984 (Patnaik et al, 1984). Including the currently described case, the average age of 9 dogs with mesenchymal chondrosarcomas was 6.9 years and 5 of the 9 reported cases were younger than five years of age (Patnaik, 1990; Southerland et al, 1993; Albers et al, 1997; LaRock et al, 1997; Madarame et al, 1998; Rhind and Welsh, 1999; Munday and Prahl, 2002; Miller et al, 2005). Although there are limited cases, mesenchymal chondrosarcomas tend to occur in relatively young and middle-aged dogs. And this tumor is more commonly seen in male dogs (8/9 cases).

According to the weights of the adult dog, the breed of dogs is classified as five groups such as toy (<5.5 kg), small (5.5∼11 kg), medium (11∼26 kg), large (26∼45 kg) and giant (≥45 kg) (Montoya et al, 2023). Chondrosarcoma in bone generally occurs in large breeds weighing 20 to 40 kg, particularly boxers, German shepherds, golden retrievers, and various mixed breeds (Thompson and Dittmer, 2017). Similarly, in the previous reports, mesenchymal chondrosarcomas were observed in large breed dogs such as German shepherds, Golden retrievers, and Mastiff dog (Patnaik, 1990; Albers et al, 1997; Madarame et al, 1998; Rhind and Welsh, 1999; Munday and Prahl, 2002). There were only two case reports of primary mesenchymal chondrosarcoma in the pericardium of a 7-year-old, 15.5 kg, standard schnauzer, a medium size dog (LaRock et al, 1997) and maxillary gingiva of a Maltese, a toy breed (Yim et al, 2021). So far, mesenchymal chondrosarcomas are very rare in toy breed dogs including Yorkshire Terrier of our present case.

Histologically, the tumor in this study composed two different features in mesenchymal chondrosarcoma: the coexistence of nests of cartilaginous tissue embedded surrounding proliferation of primitive mesenchymal cells (Madarame et al, 1998; Thompson and Dittmer, 2017). Additionally, result of immunohistochemical staining was also important key for the differential diagnosis of chondrosarcoma from other mesenchymal tumors. Positive immunoreactivity for vimentin and S-100 of the tumor cells are consistent with those reported for chondrosarcomas including mesenchymal subtype in the dog and cat (Albers et al, 1997; Madarame et al, 1998; Munday and Prahl, 2002; Romanucci et al, 2005; Yim et al, 2021).

The cause of canine extraskeletal chondrosarcomas is unknown. In human beings and dogs, some cases of extraskeletal osteosarcomas and chondrosarcoma are associated with a history of trauma (LaRock et al, 1997). However, the dog in our present case did not have any significant history associated with trauma and physical wound.

Biologically chondrosarcoma in domestic animal trends to grow more slowly, pursue a longer clinical course, and develop hematogenous metastasis later and with much less frequently than osteosarcoma (Thompson and Dittmer, 2017). Distant metastasis is less common than local invasion with this tumor. When distant metastasis does occur, it is usually to the lungs (Thompson and Dittmer, 2017). Although mesenchymal chondrosarcoma is highly malignant, only two cases of local invasion (Patnaik, 1990) and pulmonary metastasis (Munday and Prahl, 2002) were reported in dogs. In our present case, the dog lost weight about six hundred grams and showed poor prognosis after the total splenectomy. Unfortunately, the dog died three days after the surgery and the owner cremated the dog. Hence a postmortem complete necropsy was not performed. Clinical courses in this case and previous reports suggest that extraskeletal mesenchymal chondrosarcomas may have a poorer prognostic tendency than those of primary skeletal origins (Munday and Prahl, 2002; Miller et al, 2005). Adjunctive chemotherapy or radiation therapy protocols have yet to be evaluated, but surgery alone may not be curative for mesenchymal chondrosarcoma in dogs (Miller et al, 2005).

To our best knowledge, this is the first report of extraskeletal mesenchymal chondrosarcoma in a Yorkshire Terrier dog, toy breed. To establish the accurate prognosis and the treatment regime of mesenchymal chondrosacoma, more accumulated clinical data for this tumor should be warranted.

This research was supported by the 2023 education, research and student guidance grant funded by Jeju National University.

No potential conflict of interest relevant to this article was reported.