A 15-yr-old, 3.7-kg, ground cuscus (Strigocuscus gymnotis) presented with a 2-cm superficial skin abrasion on the right lateral thorax caudal to the elbow. Initial treatment with topical antiseptic (Nolvasan, Ft. Dodge Animal Health, Fort Dodge, IA, USA) produced no improvement. The lesion quickly progressed to a deeply ulcerated 3-cm area with exposed subcutaneous and skeletal muscle tissue. Multiple biopsies were taken. Pending histopathology results, the cuscus was treated with amoxicillin/clavulanic acid (Clavamox, GlaxoSmithKline, Research Triangle Park, NC, USA) at 62.5 mg p.o. b.i.d. for 14 days and meloxicam (Metacam, Boehringer Ingelheim Vetmedica, Inc., St. Joseph, MO, USA) at 0.1 mg/kg p.o. s.i.d. for 5 days.
Complete blood count (CBC) and serum biochemistry results were within normal limits at the time of biopsy. White blood cell count was 7,600/µl (reference range 1,975–11,307/µl) with 3,952/µl lymphocytes (reference range 989–6,485/µl). Radiographs revealed significant vertebral spondylosis but no evidence of tumor metastasis was evident. Histopathology was consistent with a lymphoid malignancy with possible epitheliotropism, but immunohistochemical staining for lymphoid/myeloid neoplastic processes was negative. Antibodies tested were CD45, CD45R, 3C6, 3C10, CD20, CD79A, and CD3. Negative staining was suspected to be due to the novel species tested with the standard antibodies.
Single modality oral chemotherapy was chosen based on successful outcomes of cutaneous lymphoma treatment in domestic animals and for ease of administration.1,3 One treatment with CCNU (Lomustine, Bristol-Myers Oncology, Princeton, NJ, USA) at 2.7 mg/kg p.o. (10 mg total dose) was given 8 days post biopsy. A mild decrease in appetite was noted initially. Recheck bloodwork performed 1 wk post chemotherapy revealed a decreased leukocyte count of 3100/µl, so treatment with amoxicillin/clavulanic acid (62.5 mg p.o. b.i.d.) continued for 14 days. No other adverse side effects were noted.
Treatment with 10 mg CCNU p.o. continued at approximately 3 wk intervals for a total of four doses. Complete response, defined as 100% reduction in size of measurable tumor for at least 21 days,3 was evident after the fourth dose of CCNU and the dosage interval was thus increased to every 5 wk. Repeat biopsy taken 4 mo after initial diagnosis was interpreted as cutaneous lymphoma with a strong reaction of almost all tumor cells to anti-CD3 antibody, consistent with a T-cell tumor.2 Despite this histologic evidence of neoplasia, no macroscopic lesions were present and the cuscus showed no signs of illness. CCNU was continued at 10 mg p.o. every 6 wk for another four doses.
At the time of publication, 255 days after initial clinical remission, a superficial lesion reappeared at the site of the tumor. Histopathology is again consistent with cutaneous lymphoma. No evidence of metastasis is present on radiographs. CCNU dosing will be increased to every 3 wk.
Oral chemotherapy in this case produced extended clinical remission of an isolated round cell tumor. Advantages of this treatment included minimal side effects and ease of administration. This type of therapy thus could be considered in other species with round cell neoplasia.
1. Ettinger SN. 2003. Principles of treatment for canine lymphoma. Clin. Tech. Sm. Anim. Prac. 18: 92–102.
2. Fernandez NJ, KH West, ML Jackson, BA Kidney. 2005. Immunohistochemical stains for differentiating canine cutaneous round cell tumors. Vet. Pathol. 42: 437–445.
3. Williams LE, KM Rassnick, HT Power, SE Lana, KE Morrison-Collister, K Hansen, JL Johnson. 2006. CCNU in the treatment of canine epitheliotropic lymphoma. J. Vet. Intern. Med. 20: 136–143.