Case presentation
A seven-year-old neutered male American shorthair cat was referred to the Saitama Animal Medical Center with symptoms of blepharospasm in the right eye. Ophthalmic examination revealed superficial corneal ulceration with mild eyelid restriction in the right eye, but no abnormality was observed in the left eye (Figure 1). Treatment with antibiotic and hyaluronate eye drops was started, but the corneal ulceration in the right eye did not improve at follow-up three weeks later. In addition, entropion caused by eyelid restriction persisted. Partial right eyelid tarsorrhaphy was performed to treat the corneal ulcers. However, vision was eventually lost in the right eye due to severe exposure keratitis caused by complete eyelid restriction, and resistance to retropulsion of the globe was observed at follow-up. Orbital disease was suspected from these clinical findings. Ultrasound examination was performed, but no apparent mass was observed in the globe or in the orbit. (Figure 2A). Oral prednisolone (5 mg/head, once daily) was prescribed for suspected orbital inflammation but was ineffective, and the dose was tapered off and eventually discontinued.
Given the lack of improvement in clinical symptoms by medical treatment, surgical resection following computed tomography (CT) was scheduled on day 138 after initial presentation. CT revealed a space-occupying lesion in the right orbit, with infiltration extending from the eyelid to the lips (Figure2B). There were no osteolytic lesions in the orbital bone and no sign of abdominal or thoracic metastasis. Following the CT examination, orbital exenteration of the right eye was performed. The orbit contained multiple nodular lesions, and these were removed to the extent possible. All specimens were fixed in 10% formalin, embedded in paraffin, sectioned at 4 µm, and subject to hematoxylin and eosin (HE) and immunohistochemical staining.
Histopathological examination of HE stained sections revealed the proliferation of atypical spindle tumor cells infiltrating the skeletal muscle in the orbital tissue with thin collagenous materials between spindle cells and moderate lymphoplasmacytic cell infiltration (Figure3A), but there was no invasion into the globe. Neoplastic spindle cells resemble reactive fibroblasts or myofibroblasts with mild anisocytosis and anisokaryosis. These spindle cells have a moderate amount of elongated eosinophilic cytoplasm and ovoid nuclei with finely stripped chromatin and one to two nucleoli. There were 4–5 mitotic figures in tumor cells per ten high-power fields. Immunohistochemistry showed positive staining for smooth muscle actin (SMA) in the tumor cells (Figure3B). Based on these histopathological findings, the tumors were diagnosed as FROMS.
After surgery, the mass in the right lip enlarged, leading to feeding difficulty. A gastrostomy tube was placed under general anesthesia. Three weeks after surgery, toceranib 2.17 mg/kg was initiated three times per week as adjuvant chemotherapy. Toceranib administration was continued for one month. However, the residual tumor continued to increase in size, and adjuvant chemotherapy was deemed ineffective and was discontinued. Subsequently, bleeding from the tumor occurred, which severely deteriorated the cat’s quality of life. Eventually, the cat died four months after surgery, 257 days after initial presentation.