Metastatic synovial cell sarcoma in two cats

Case 1

A 15-year-old, female neutered, domestic long-hair cat presented with a history of elevated serum liver activities of unknown cause. A mass, measuring 2.5 × 2.0 cm, encompassing the dorsolateral aspect of the left tibiotarsal joint was detected during physical examination. Lameness was not apparent, palpation of the mass did not elicit a painful response and regional lymph nodes were not palpable. Haematology and serum thyroxine concentrations were within the normal reference ranges. Serum biochemical abnormalities included elevated alanine transferase [282 IU L⁻¹, reference range (RR) 30–100 IU L⁻¹], aspartate transferase (150 IU L⁻¹, RR 15–50 IU L⁻¹) and gamma glutamyltransferase (4 IU L⁻¹, RR 0–2 IU L⁻¹) activities. Laparoscopic biopsies of the liver were submitted for histopathology and consistent with lymphocytic–plasmocytic cholangiohepatitis.

Fine-needle aspiration, incisional biopsy and radiographs of the left hock were performed for diagnostic and staging purposes. Cytology of the fine-needle aspirate was consistent with granulomatous inflammation and radiographs revealed a soft tissue swelling along the dorsolateral aspect of the left tarsus with no underlying osseous involvement (Fig. 1). There was no evidence of metastasis on three-view thoracic radiographs. The mass was diagnosed as a SCS based on histopathological examination of tissue obtained by incisional biopsy.

The cat was premedicated with midazolam and hydromorphone, induced with propofol, and maintained on isoflurane and oxygen. Intraoperative analgesia consisted of an epidural injection of morphine and bupivacaine, and a continuous rate infusion of ketamine (2 µg kg⁻¹ min⁻¹ intravenously) and fentanyl (2 µg kg⁻¹ h⁻¹ intravenously). Cephazolin (25 mg kg⁻¹) was administered intravenously at induction of general anaesthesia. A left pelvic limb amputation was performed with disarticulation of the coxofemoral joint (Fig. 2). Postoperative analgesia included a continuous rate infusion of hydromorphone (0.01 µg kg⁻¹ min⁻¹ intravenously) and ketamine (2 µg kg⁻¹ min⁻¹ intravenously) for 48 h, oral morphine (2.7 mg every 8 h per os) for 3 days, and piroxicam (1 mg every 48 h per os) for 10 days.

Histopathological examination of the tarsal mass and ipsilateral popliteal lymph node was performed. Within the local mass, neoplastic round-to-polygonal cells, with moderately pleomorphic round nuclei and abundant eosinophilic cytoplasm, formed broad sheets with interspersed, loose collagenous material. Cleft-like spaces were absent. The nuclei were frequently bizarre with one nucleolus and greater than 30 mitotic figures per 10 high power fields. The percentage of tumour necrosis was estimated at 10% and the tumour was poorly demarcated. There were few giant cells and a moderate number of multinucleated cells (=three nuclei per cell). Approximately 30% of the popliteal lymph node was effaced with the same neoplastic cells observed in the primary mass, whereas the remainder of the node contained abundant lymphoid follicles interspersed between sheets of neoplastic cells. A grade III SCS was diagnosed on the basis of the grading scheme used in dogs with SCS (Vail et al., 1994). These findings were consistent with stage III_A (T1 N₁ M₀) SCS, according to a modified staging system for soft tissue sarcomas proposed by MacEwen et al. (2001).

The cat was treated with adjunctive chemotherapy. Doxorubicin (1 mg kg⁻¹ intravenously) was administered every 3 weeks for five treatments. An accidental overdose of doxorubicin was administered on the fifth dose (3.2 mg kg⁻¹ intravenously). The cat was treated with ondansetron (0.3 mg every 12 h per os) for 6 days and enrofloxacin (20 mg every 24 h per os) for 14 days. Serial haematology revealed lymphopaenia (0.3 × 10³ µL⁻¹, RR 1.5–6.0 × 10³ µL⁻¹) and neutropaenia (1.3 × 10³ µL⁻¹, RR 2–12 × 10³ µL⁻¹) with a mild left shift (band neutrophils 0.3 × 10³ µL⁻¹, RR <0.1 × 10³ µL⁻¹) and a low normal platelet count (211 × 10³ µL⁻¹, RR 200–500 × 10³ µL⁻¹) 7 days postdoxorubicin administration. Granulocyte colony-stimulating factor was administered at this time. Within 4 days, neutropaenia had resolved (10.2 × 10³ µL⁻¹), platelet count increased (488 × 10³ µL⁻¹) and the lymphopaenia had improved although was still below the reference range (0.8 × 10³ µL⁻¹).

The cat was examined 316 days postoperatively. A firm, non-painful mass, measuring 1.5 × 3.0 cm, was present at the amputation site. Local recurrence of the SCS at the amputation stump was confirmed by fine-needle aspiration of the mass. Two lung lesions, consistent with pulmonary metastases, were detected on three-view thoracic radiographs (Fig. 3) at this time. Chronic renal failure, possibly secondary to the overdose of doxorubicin (O'Keefe et al., 1993) or age-related disease, was suggested by the presence of a non-regenerative anaemia (packed cell volume 26%, RR 30–46% and reticulocyte count 11 680 µL⁻¹, RR 0–50 000 µL⁻¹) and azotaemia (blood urea nitrogen 89 mM, RR 16–35 mM and creatinine 3.9 mM, RR 1.3–2.6 mM). The anaemia and azotaemia persisted, despite management with potassium gluconate (2 mEq every 12 h per os) and subcutaneous fluid administration, and the cat was euthanized 444 days postoperatively as a result of progressive and unresponsive chronic renal failure.

Case 2

A 12-year-old, male neutered, domestic short-haired cat presented with chronic asthma and a 5-week history of right pelvic limb swelling and lameness. On physical examination, the cat was overweight (7.6 kg body weight) with a grade 4 to 5 right pelvic limb lameness and diffuse swelling distal to the right stifle. Haematology and serum biochemistry results were within normal limits. A peribronchial pulmonary pattern with atelectasis of the right middle lung lobe, both consistent with chronic bronchitis secondary to asthma, was evident on three-view thoracic radiographs. Radiographs of the right pelvic limb revealed intra- and extra-articular mineralization of the stifle. Ultrasonographic examination of the right stifle confirmed the presence of areas of poorly circumscribed soft tissue mineralization and also identified an enlarged popliteal lymph node. Ultrasound-guided fine-needle aspirates of the caudal stifle region and popliteal lymph node were performed. An undifferentiated sarcoma with ipsilateral popliteal lymph node metastasis was suspected on the basis of cytological examination of these aspirates. The cat was treated with albutenol for 3 days in an attempt to improve respiratory function prior to anaesthesia and surgery.

The cat was premedicated with atropine and hydromorphone, induced with midazolam and ketamine, and maintained on isoflurane and oxygen. Bronchoscopy and bronchoalveolar lavage were performed prior to surgery. Bronchoscopy revealed a flaccid airway with increased secretions and polypoid bronchial masses consistent with bronchomalacia and polypoid hyperplasia. Infectious organisms were not identified from aerobic and mycoplasmal cultures of respiratory secretions collected by bronchoalveolar lavage. Intraoperative analgesia consisted of an epidural injection of morphine and bupivacaine and a continuous rate infusion of ketamine (2 µg kg⁻¹ min⁻¹ intravenously) and fentanyl (2 µg kg⁻¹ h⁻¹ intravenously). Cephazolin (25 mg kg⁻¹) was administered intravenously at induction of general anaesthesia. A right pelvic limb amputation was performed with disarticulation of the coxofemoral joint. The semimembranosus and semitendinosus muscles were surrounded by oedematous tissue, which extended to the level of the ischiatic tuberosity. Postoperative analgesia consisted of a continuous rate infusion of hydromorphone (0.0125 µg kg⁻¹ min⁻¹ intravenously) and ketamine (2 µg kg⁻¹ min⁻¹ intravenously) for 24 h and a transdermal fentanyl patch (25 µg) for 3 days.

A diagnosis of an incompletely resected, grade III SCS with ipsilateral lymph node metastasis was made on the basis of histopathological examination of the stifle mass and popliteal lymph node. Both the mass and popliteal lymph node contained highly pleomorphic round-to-polygonal cellswith marked anisocytosis, moderate anisokaryosis, multiple prominent nucleoli, greater than 30 mitotic figures per 10 high power fields, few giant cells and numerous multinucleated giant cells (4, 5). The degree of tumour necrosis was estimated at 30% and cleft-like spaces were present. The tumour was poorly demarcated and the cranial and caudoproximal margins of the amputated limb contained scattered nests of neoplastic cells approximately 5 mm distant to the mass, consistent with incomplete resection. On the basis of clinical and histological findings, a stage III_A (T1 N₁ M₀) SCS was diagnosed.

The cat was scheduled to receive doxorubicin every 3 weeks for five treatments. However, 7 days after the second dose of doxorubicin (1 mg kg⁻¹ intravenously) and 41 days postoperatively, the cat died following an acute episode of respiratory arrest. Necropsy was performed and revealed firm and adherent thromboemboli in the pulmonary arteries of the cranioventral lung lobes, marked and diffuse bronchial thickening, and no gross evidence of cardiac abnormalities. The cause of pulmonary thrombosis remains undetermined as there was no gross or histological evidence of cardiac disease, the pulmonary thrombosis was not neoplastic in origin, and the cat was in otherwise good physical condition.