Oral leiomyosarcoma in a dog

INTRODUCTION

Canine oral tumor is relatively common accounting for 6% of all tumors in dogs. The most common oral tumors in dogs include malignant melanoma, squamous cell carcinoma, fibrosarcomas [1-3]. Leiomyosarcoma is a malignant mesenchymal tumor originated from smooth muscle [4]. Leiomyosarcoma constitutes 20 to 30 per cent of all intestinal neoplasms in dogs [5], however, oral leiomyosarcoma is scare owing to paucity of smooth muscle structures in this location [6]. Therefore, no specific reference to their diagnosis, management and prognosis has been reported up to date [7]. Herein, we report maxillary leiomyosarcoma in a dog confirmed by immunohistochemistry.

CASE REPORT

A 13-year-old, neutered male Poodle was administered to veterinary medical teaching hospital in Gyeongsang National University for left maxillary mass. Initially, a small-sized mass (<1 cm) was found on the upper body of the maxilla, and it enlarged rapidly for the last 4 weeks. It was not responsive to antibiotics prescribed from the local veterinary clinic, and recently accompanied by dysphagia, hyporexia, and hemorrhage. Oral examination revealed a 4.8 cm × 2.5 cm-sized hard and immobile mass was observed on the left maxilla (Fig. 1A). Left prescapular lymph node was also enlarged, but no abnormalities in core temperature, purse rate, and respiratory rate were found. A complete blood count revealed normocytic normochromic regenerative anemia (hematocrit [HCT, 33.6%; reference range, 37.3%–61.7%; reticulocyte count, 117.6 × 10³/μL), leukocytosis (18.07 × 10³/ μL; reference range, 5.05–16.76 × 10³/μL), and thrombocytosis (651 × 10³/μL; reference range, 148–484 × 10³/μL). Serum biochemistry analysis revealed hyperglobulinemia (4.8 mg/dL; reference range, 2.5–4.5 mg/dL) (Table 1). Thromboelastgraphy (TEG) to determine the risk of hypercoagulability of the tumor revealed high MA, short K evaluated as hypercoagulable state. Cytological evaluation of the maxillary mass showed predominant spindle cells met malignancy criteria of tumor cells, including coarse chromatin, high N/C ratio, nuclear molding, macro/multi-nucleoli with cigar-shaped nucleus (Fig. 1B). Cytological evaluation of the enlarged left scapular lymph node by fine needle aspiration also revealed metastasis-associated malignant cells. Radiography of the skull showed lysis of the nasopalatine bone, and mineral radiopacity in the mass (Fig. 2A). Computed tomography showed soft tissue attenuating mass from the left incisor teeth to the left retrobulbar space with loss of nasal bone, palatine bone and orbital medial wall (Fig. 2B). The histopathological examination showed the irregularly arranged spindle-shaped cells, and oval or elongated nuclei of the tumor cells. The nucleolus is distinct and moderate cellular polymorphism is observed. Mitotic figures are occasionally observed (Fig. 3). The tumor cells are positive to vimentin, desmin, α-smooth muscle actin when immunohistochemistry was performed using anti-vimentin, anti-desmin, anti-alpha smooth muscle actin (α-SMA) (Santa Cruz Biotechnology, Dallas, TX, USA) antibodies. In Masson’s trichrome stain, tumor cells are stained as red (Fig. 4). Overall, histopathologic exam and immunohistochemistry confirmed canine oral leiomyosarcoma. However, owner did not consent surgical resection. Esophageal tubing for palliative therapy was applied and follow up was lost.

Fig. 1. Macroscopic and microscopic examination of the oral leiomyosarcoma. (A) A hard and immobile mass located on the left maxilla of the oral leiomyosarcoma. (B) Cytologic examination of the mass showing predominant malignant spindle-shaped cells satisfying malignancy criteria of tumor cells.

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Fig. 2. Diagnostic imaging analysis of the dog with oral leiomyosarcoma. (A) Radiography of the skull showed bone lysis, and mineral opacity. (B) Computed tomography showed soft tissue attenuating mass from the left incisor teeth to the left retrobulbar space with loss of nasal bone, palatine bone and orbital medial wall (arrow).

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Fig. 3. Histopathologic examination of the mass. (A) the spindle-shaped cells are irregularly arranged. (B) The nuclei of the tumor cells are oval or elongated. The nucleolus of the tumor cells is distinct, and cellular polymorphism is moderated. Mitotic figures are occasionally seen. H&E, Original magnifications: 100 × (A), 400 × (B).

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Fig. 4. Immunohistochemistry and Masson’s trichrome stain of the mass. (A) The tumor cells are positive to vimentin, (B) desmin, (C) α-smooth muscle actin. (D) In Masson’s trichrome stain, tumor cells are stained as red. A few Fibroblasts and some collagen in the vessels or connective tissue are stained as blue. Original magnifications: 100 × (D), 200 × (A, B, C).

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DISCUSSION

Leiomyosarcoma is malignant mesenchymal tumor of smooth muscle. The most common site of the leiomyosarcoma is gastrointestinal tract, such as stomach, esophagus, small intestine, and colorectum in dogs [1, 8-11]. Oral leiomyosarcoma is rare in dogs due to lack of smooth muscle tissue in the oral cavity. Several reports suggested that the major sources of smooth muscle in the oral cavity are the walls of blood vessels or displaced embryonal tissue, the vascular system of bone or accessory salivary glands [6, 12]. Since it is not commonly encountered in veterinary clinic, leiomyosarcoma should be confirmed by histopathology and immunohistochemistry. The cells are typically composed of long, plump spindle cells, which have cytoplasm with oval blunt-ended nuclei, perinuclear vacuoles, and frequent nuclear chromatin crossbars, but collagenous stroma is little. Leiomyosarcomas are positive for vimentin, a-smooth muscle actin as well as desmin in the immunohistochemistry [13, 14]. The present case present oral mass on the left maxilla, and leiomyosarcoma was confirmed by immunohistochemistry. Sarcomas can be the top of the differential list for cigar-like nuclear morphology and spindle cells met malignant criteria of the tumor cells. In case of oral sarcomas, leiomyosarcoma can be considered if cytological analysis are consistent with smooth muscle-originated cells.

In human, the prognosis of leiomyosarcoma is poor, with a high percentage of recurrence or metastasis. The most common sites of metastasis include the lungs, bone, brain and the lymph node [15]. The most effective treatment of the leiomyosarcoma is radical surgical excision with adequate margins [10, 16]. For inoperable tumors or those in difficult sites such as the mandibular condyle or maxillary sinus, radiotherapy can be used in addition to surgery [17]. Chemotherapy appeared to be ineffective unless it was used as a palliative measure in patients with widespread metastatic disease [18]. Kapatkin et al. reported that the prognosis in dogs with leiomyosarcoma of the spleen, stomach, small intestine, and especially the cecum is good if surgery is performed [5]. Though it has not been sufficiently studied in dogs, the site of the leiomyosarcoma is more important for prognosis when compared to human study: those arising in a superficial cutaneous localization have the best prognosis [15] whereas bony involvement is a potential negative prognostic indicator in human [19]. In the present case, there was an extensive soft tissue mass from the left incisor teeth to the left retrobulbar space with bone invasion, thus complete excision with surgery was impossible. Unfortunately, proper treatment options were not applied, but the prognosis might not be good considering given the size and the location of the lesion.