Korean Journal of
Veterinary Service

Fibrosarcoma is a malignant mesenchymal cancer caused by abnormal proliferation of fibroblasts. In dogs, it commonly occurs in the skin, subcutaneous tissue, and oral tissue, rarely involving other tissues (Goldschmidt and Hendrick, 2002). Currently, various treatment modalities are available for the treatment of canine fibrosarcoma, including surgical removal, chemotherapy, radiotherapy, and immunotherapy (Milovancev et al, 2016). Among the available chemotherapy options, metronomic therapy, a treatment method that involves frequent administration of low doses of anti-cancer drugs, is becoming increasingly popular.

Toceranib is a representative metronomic anti-cancer drug (Frezoulis and Harper, 2022). Metronomic chemotherapy is widely used in cases where surgery or radiotherapy is difficult, or where anti-cancer drugs are administered as ‘maintenance’ therapy (Gardner et al, 2015). Metronomic chemotherapy is expected to be less toxic than general chemotherapy; however, limited number of studies have reported on its effectiveness of side effects in various tumors.

To our knowledge, this is the first case report describing the clinical symptoms, diagnosis, treatment progress, and prognosis of toceranib chemotherapy for simultaneous hepatic and splenic fibrosarcomas in a 12-year-old neutered ale Maltese dog. The report aimed to prospectively evaluate the clinical benefits of toceranib therapy for metastatic fibrosarcomas of the liver in dogs.

A 12-year-old neutered male Maltese dog weighing 3.9 kg was brought to the animal hospital with a history of general weakness, loss of appetite, generalized alopecia, pale skin and oral mucosa, and a palpable abdominal mass. The dog had undergone a surgery for the removal of bladder stone and skin lipoma at an animal hospital approximately 1 year ago. During the physical examination, there was a clearly palpable large abdominal mass with rebound pain and lymph node enlargement was not observed. In addition, body temperature was within the normal range. Blood tests, radiography, and abdominal ultrasonography were performed (Fig. 1A, 1B). A complete blood count (CBC) showed low levels of hematocrit (HCT), indicating anemia (32.7%; reference range, 39∼56%). Radiography and ultrasonography revealed the presence of multiple large masses in the liver and spleen, with a small amount of ascites. The largest liver mass diameter was 34.82 mm on ultrasonography (Fig. 1C).

Figure 1. (A) X-ray, lateral view, of the hepatic fibrosarcoma before taking toceranib (arrow). (B) X-ray, ventrodorsal (VD) view, of the hepatic fibrosarcoma before taking toceranib (arrow). (C) Ultrasonography of the hepatic fibrosarcoma before taking toceranib. (D) X-ray, lateral view, of the hepatic fibrosarcoma after 30 days of taking toceranib (arrow). (E) X-ray, VD view, of the hepatic fibrosarcoma after 30 days of taking toceranib (arrow). (F) Ultrasonography after 30 days of taking toceranib.

The following day, splenectomy and liver biopsy were performed, and histological examination revealed metastatic fibrosarcoma of unknown origin in the liver and spleen (Fig. 2). In high-grade hepatic fibrosarcoma, the tumor cells exhibited a relatively abundant cytoplasm with prominent intracytoplasmic vacuoles. Additionally, the nuclei showed atypical morphology with hypertrophied and severely anisokaryotic features. Multiple prominent nucleoli were observed within the tumor cell nuclei, and multinucleated cells were frequently present. Mild infiltration of inflammatory cells was also observed. In high-grade splenic fibrosarcoma, the tumor cells exhibited a round-oval morphology with hypertrophied and severely atypical nuclei. Additionally, numerous prominent nucleoli were observed within the tumor cell nuclei, and multinucleated cells were frequently observed. Blood tests, radiography, and ultrasonography were performed every 10 days after splenectomy. The owner refused further investigations, such as computed tomography and hepatectomy, and treatment options such as doxorubicin chemotherapy for economic reasons. Therefore, toceranib phosphate was selected as a safe, economical, and convenient adjuvant chemotherapeutic agent. The dog was administered toceranib phosphate (10 mg/dog, PO, q48h) and no additional drugs were administered. However, the size and number of liver masses continuously increased, as observed using ultrasonography and radiography while the dog was on continued toceranib therapy (Fig. 1D∼F). During toceranib therapy, ultrasound examinations were obtained approximately every 15 days and tumor response measurements were determined according to VCOG (Veterinary Cooperative Oncology Group) Response Evaluation Criteria for Solid Tumors in Dogs (v1.0) (RECIST) (Table 1) (Nguyen et al, 2015). After approximately 30 days of toceranib therapy, the maximum diameter of the largest mass increased to 70.37 mm (Fig. 1F). A repeat CBC showed persistently elevated white blood cell (WBC) count, while HCT levels gradually decreased. Enzyme levels on the liver function test (alkaline phosphatase (ALP), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), cholesterol (CHOL)) increased, whereas the serum concentration of interferon-gamma (IFN-γ), a representative anti-tumor cytokine, remained unchanged (Table 2). No gastrointestinal side effects such as diarrhea or vomiting were observed during the toceranib treatment. However, the dog’s poor condition persisted, and it died after approximately 43 days of continuous toceranib therapy.

Table 1 . Response evaluation of toceranib therapy according to VCOG guideline.

Time-points	Tumor	New lesions	Overall response
15 days follow-up after therapy	PD	Yes	PD
30 days follow-up after therapy	PD	Yes	PD

CR, complete response; PR, partial response; SD, stable disease; PD, progressive disease..

Table 2 . Changes in blood test results and serum cytokine levels spanning 35 days since the day of splenectomy (Day 0).

	Reference range	Day 0	Day 7	Day 17	Day 27	Day 35
WBC	6.0∼17.0 (109/L)	16.3	25.9	20.8	18.4	27.7
RBC	5.5∼8.5 (1012/L)	5.27	3.09	3.23	3.24	2.72
Hb	11.0∼19.0 (g/dL)	11.8	7.9	8.2	7.6	7.3
HCT	39.0∼56.0 (%)	32.7	20.5	22.4	21.9	19.1
Platelets	117∼460 (109/L)	316	202	356	343	191
ALP	18.0∼214 (U/L)	92	161	213	286	419
ALT	12.0∼101 (U/L)	48	82	91	146	179
ALB	2.2∼3.9 (g/dL)	2.3	2.2	2.2	2.4	2.0
BUN	7.0∼29 (mg/dL)	15.9	29.1	25.4	22.1	21.6
Ca	9.0∼13.4 (mg/dL)	9.8	9.6	10.1	10.9	10.6
CHOL	100∼330 (mg/dL)	267	305	450	450	414
GGT	0∼7.0 (U/L)	5	5	5	16	34
Globulin	2.3∼4.6 (g/dL)	3.4	3.2	3.7	3.2	3
GLU	74∼146 (mg/dL)	71	83	88	89	91
TBIL	0∼1(mg/dL)	0.12	0.18	0.13	0.22	0.21
Na+	138∼158 (mmol/L)	147	153	148	145	151
Cl−	107∼122 (mmol/L)	121	128	118	112	119
K+	3.2∼5.5 (mmol/L)	5	4.3	4.5	5.3	5.2
IFN-γ	0.026∼2.367 (ng/mL)	-	0.201	0.201	0.203	0.204

WBC, white blood cell; RBC, red blood cell; Hb, hemoglobin; HCT, hematocrit; ALP, alkaline phosphatase; ALT, alanine aminotransferase; ALB, albumin; BUN, blood nitrogen; Ca, total serum calcium; CHOL, cholesterol; GGT, gamma-glutamyl transferase; GLU, glucose; TBIL, total bilirubin; Na⁺, sodium ion; Cl⁻, chloride ion; K⁺, potassium ion; IFN-γ, interferon-gamma..

Figure 2. (A) Intraoperative image of the hepatic fibrosarcoma (arrow). (B) Whole slide section of the hepatic fibrosarcoma. (C) High magnification of the hepatic fibrosarcoma cells (arrow). (D) Splenic fibrosarcoma tissue (arrow, *). (E) Whole slide section of the splenic fibrosarcoma. (F) High magnification of the splenic fibrosarcoma cells (arrow).

To the best of our knowledge, this is the first report of the use of toceranib phosphate as a single agent for a canine hepatic fibrosarcoma. Fibrosarcoma of the liver and spleen in dogs have an extremely low incidence, and research on their treatment is lacking (Patnaik et al, 1980; Spangler et al, 1994; Day et al, 1995). In particular, hepatic fibrosarcoma is a rare hepatic neoplasm (Patnaik et al, 1980). In veterinary medicine, traditional cancer treatments include radiation therapy and hemotherapy. Metronomic chemotherapy is defined as the oral administration of low-dose chemotherapy on a regular schedule and has several advantages, such as better tolerability, low cost, convenience, low probability of inducing drug resistance, and ability of being combined with other therapies. Representative metronomic chemotherapeutic drugs used in veterinary medicine include cyclophosphamide, chlorambucil, and toceranib (Gardner et al, 2015).

Toceranib phosphate is an anti-cancer agent that primarily targets the receptor tyrosine kinases stem cell factor receptor (KIT) protein and affects vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), and FMS-like tyrosine kinase-3 (Flt-3) (Frezoulis and Harper, 2022). Vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) play key roles in cancer angiogenesis in solid tumors (Carmeliet, 2005). Moreover, VEGF plays an important role in cancer growth and metastasis (Hisada and Mackman, 2019). Toceranib has attracted attention as an anti-angiogenic drug because it targets VEGF and PDGF (Frezoulis and Harper, 2022). Additionally, toceranib reportedly depletes regulatory T lymphocytes (Tregs), potentially enhancing anti-tumor immunity (Mitchell et al, 2012).

To date, several studies have reported the clinical effectiveness of toceranib in various cancers such as mast cell tumor, soft tissue sarcoma, melanoma when used as a single agent of in combination therapy with other anti-cancer drugs (Jang et al, 2015; Pan et al, 2016; Laver et al, 2018; Frezoulis and Harper, 2022). However, studies evaluating its effectiveness in hepatic fibrosarcoma treatment are lacking. In human medicine, chemotherapeutic agents such as vincristine, actinomycin, and doxorubicin are utilized for treatment (Kim et al, 2007). Upon the owner’s request, this chemotherapy was not administered in this case. Thus, we chose toceranib, an oral chemotherapy that offers advantages such as reasonable price, minimal side effects, and convenient for administration at home. In this case, toceranib was administered as a single agent to a dog with hepatic fibrosarcoma; however, the tumor size and number increased continuously. While receiving toceranib, the level of serum IFN-γ, a representative anti-cancer cytokine, remained unchanged (Calvalido et al, 2016).

Future studies should focus on identifying the receptor tyrosine kinases proteins that are mainly expressed in canine hepatic fibrosarcoma tissues. This will enable development of various targeted therapies against liver cancer. Moreover, the efficacy of toceranib in combination with other anti-cancer drugs should be evaluated, which may potentially be a clinically beneficial chemotherapy strategy for canine hepatic fibrosarcoma.

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