Radiation therapy for incompletely resected canine mast cell tumors

Autologous blood pleurodesis for surgical pneumothorax and outcome with multimodal cancer treatment in a dog with primary pulmonary mast cell tumor

A dog underwent lung lobectomy for removal of a mass. Histopathology was consistent with narrow resection of a mast cell tumor. Postoperative pneumothorax was successfully treated using autologous blood pleurodesis. Progression of disease despite adjunctive treatment with several chemotherapetutic agents and radiation therapy resulted in euthanasia approximately 4 months postoperatively.

Diagnosis, Prognosis and Treatment of Canine Cutaneous and Subcutaneous Mast Cell Tumors

Mast cell tumors (MCTs) are hematopoietic neoplasms composed of mast cells. It is highly common in dogs and is extremely important in the veterinary oncology field. It represents the third most common tumor subtype, and is the most common malignant skin tumor in dogs, corresponding to 11% of skin cancer cases. The objective of this critical review was to present the report of the 2nd Consensus meeting on the Diagnosis, Prognosis, and Treatment of Canine Cutaneous and Subcutaneous Mast Cell Tumors, which was organized by the Brazilian Association of Veterinary Oncology (ABROVET) in August 2021. The most recent information on cutaneous and subcutaneous mast cell tumors in dogs is presented and discussed.

Outcomes of adjunctive radiation therapy for the treatment of mast cell tumors in dogs and assessment of toxicity: A multicenter observational study of 300 dogs

Background

Radiation therapy is commonly used as an adjunct to incomplete surgical excision in dogs with mast cell tumors (MCT), but the optimal dose and fractionation regimen have yet to be determined.

Hypothesis

We assessed outcomes (time to local recurrence, patient survival and toxicity) of a large population of dogs with MCT that received adjunctive radiation therapy.

Animals

Three hundred dogs with 302 MCT treated using adjunctive radiation therapy.

Methods

Retrospective observational study. Clinical records of 4 veterinary radiation centers were reviewed.

Results

Local recurrence rates were similar regardless of radiation protocol with 6.6% of patients developing recurrent cutaneous MCT at a median of 526 days. Local recurrence rate was similar between high and low‐risk MCT. Mast cell tumor related death was reported in 19% of all dogs, with 13% of dogs with low‐risk MCT dying of their disease compared to 29% of dogs with high‐risk MCT. No SC MCT (SCMCT) recurred after radiation therapy and only 7% of dogs with SCMCT were reported to have died of their disease. Mild late toxicity was common in both protocols and severe late toxicity occurred in 1.9% of dogs many years after treatment.

Conclusions and Clinical Importance

Our study supports the use of adjunctive radiation for the long‐term control of incompletely or narrowly excised cutaneous and SCMCT in dogs. More moderate dose and fractionation protocols may be appropriate in the adjunctive treatment of low‐risk MCT in dogs. Large multicenter prospective studies are required to establish the optimal dose and fractionation for MCT of different risk categories.

World Small Animal Veterinary Association Global Dental Guidelines

Dental, oral, and maxillofacial diseases are some of the most common problems in small animal veterinary practice. These conditions create significant pain as well as localized and potentially systemic infection. As such, the World Small Animal Veterinary Association (WSAVA) believes that un- and under treated oral and dental diseases pose a significant animal welfare concern. Dentistry is an area of veterinary medicine which is still widely ignored and is subject to many myths and misconceptions. Effective teaching of veterinary dentistry in the veterinary school is the key to progression in this field of veterinary medicine, and to the improvement of welfare for all our patients globally. These guidelines were developed to provide veterinarians with the information required to understand best practices for dental therapy and create realistic minimum standards of care. Using the three-tiered continuing education system of WSAVA, the guidelines make global equipment and therapeutic recommendations and highlight the anaesthetic and welfare requirements for small animal patients. This document contains information on common oral and dental pathologies, diagnostic procedures (an easily implementable and repeatable scoring system for dental health, dental radiography and radiology) and treatments (periodontal therapy, extractions). Further, there are sections on anaesthesia and pain management for dental procedures, home dental care, nutritional information, and recommendations on the role of the universities in improving veterinary dentistry. A discussion of the deleterious effects of anaesthesia free dentistry (AFD) is included, as this procedure is ineffective at best and damaging at worst. Throughout the document the negative effects of undiagnosed and/or treated dental disease on the health and well-being of our patients, and how this equates to an animal welfare issue, is discussed.

Ultrasound is a poor predictor of early or overt liver or spleen metastasis in dogs with high-risk mast cell tumours

Conflicting evidence exists regarding the importance of routine abdominal ultrasound (US) with hepatic and splenic fine needle aspiration (FNA) cytology during staging of canine mast cell tumours (MCT). The objective of this study was to correlate ultrasonographic and cytologic findings in dogs with strictly defined high-risk MCTs and to determine the influence on outcome. Our hypothesis was that US poorly predicts visceral metastasis in high-risk MCTs and that early metastasis is associated with improved outcome when compared to overt metastasis. US of liver and spleen correlated to cytologic results, categorized as no metastasis, early metastasis or overt metastasis. Of 82 dogs prospectively enrolled, 18% had early visceral metastasis and 7% had overt metastasis on cytology; 67% with visceral metastasis had regional LN metastasis. US was a poor predictor of metastasis with sensitivity, specificity, positive predictive value and negative predictive value for the spleen of 67%, 68%, 21% and 94%, respectively and for the liver of 29%, 93%, 56% and 82%, respectively. Median time to progression (TTP) for dogs with no metastasis, early metastasis and overt metastasis was not reached, 305 and 69 days, respectively (P < .001). Median survival time (MST) for the 3 groups were not reached, 322 and 81 days, respectively (P < .001). High Patnaik or Kiupel grade, early metastasis, overt metastasis and adequate local control were significantly associated with outcome. Early visceral metastasis was associated with poorer outcome compared to dogs without metastasis, however, a subset of dogs experienced long-term control.

Treating the locoregional lymph nodes with radiation and/or surgery significantly improves outcome in dogs with high-grade mast cell tumours

High-grade canine mast cell tumours (HG-MCT) have a high rate of locoregional relapse. In this study, dogs with HG-MCT treated with radiation therapy (RT) were retrospectively evaluated to determine the benefit associated with treating the locoregional lymph nodes (LNs). Forty-two dogs were included. Variables assessed for association with overall survival (OS) and progression-free survival (PFS) included WHO stage, tumour location and size, LN irradiation (prophylactic, therapeutic or none), LN treatment (yes or no), LN status at RT (metastatic or nonmetastatic) and RT intent (definitive vs palliative). Lower-stage disease at irradiation was significantly associated with prolonged median PFS (425 vs 125 days for stage 0 vs 1-4), and OS (615 vs 314 days for stage 0 vs 1-4). Having any LN treatment and definitive RT were both significantly associated with prolonged OS. In order to evaluate the role of LN irradiation, dogs were divided into subgroups: (a) stage 0 at irradiation with no LN treatment (n = 14), (b) stage 0 at irradiation with prophylactic LN irradiation (n = 6), (c) stage 0 at irradiation but previously stage 2 (n = 5) and (d) stage >0 at irradiation (n = 17). Prophylactic LN irradiation significantly prolonged PFS (>2381 vs 197 days; group B vs A). Interestingly, dogs that were stage 2 and had LN treatment (C) had prolonged OS vs dogs with negative LNs and no LN treatment (A) (1908 vs 284 days; P = .012). This study confirms that prophylactic and therapeutic LN irradiation in dogs with HG-MCT is beneficial and improves outcome.

Haematologic toxicity in dogs with mast cell tumours treated with vinblastine/prednisolone chemotherapy with/without radiotherapy

OBJECTIVES

To determine whether dogs with surgically excised mast cell tumours receiving a vinblastine/prednisolone chemotherapy protocol in combination with radiation therapy are at greater risk of myelosuppression than patients receiving the chemotherapy protocol alone.

MATERIALS AND METHODS

Retrospective study of clinical records of dogs with mast cell tumours that, subsequent to surgical excision, had received combination vinblasine/prednisolone chemotherapy. Dogs were assigned to two groups: those treated with adjunctive radiotherapy and vinblastine/prednisolone (RT group) and those treated with surgery followed by vinblastine/prednisolone alone (control group). Haematology results were compared between groups.

RESULTS

Forty-three cases and 43 controls of similar breed, age and bodyweight were included. Concurrent radiation and vinblastine chemotherapy did not appear to increase the risk of neutropenia, which was observed in 18.6 and 23.2% of cases in the RT and control groups, respectively.

CLINICAL SIGNIFICANCE

Radiation and vinblastine chemotherapy can be safely combined in dogs with mast cell tumours without increasing the risk of clinically important myelosuppression.

Acute radiotherapy toxicity in 57 dogs with gross and microscopic mast cell tumours

Mast cell tumours (MCTs) are commonly treated with radiation therapy, most often in a microscopic disease setting. Poorer outcomes are expected in patients with gross disease, and irradiation of gross disease may be associated with greater toxicity. The aim of this study was to compare acute radiation adverse events (AE) in dogs with gross and microscopic MCTs receiving radiotherapy. Fifty-seven dogs were included, 28 with gross disease and 29 with microscopic. In order to assess mucosal and skin toxicity, patients were assigned to 2 groups: head (29 patients, 14 patients with gross and 15 microscopic) and other sites (28 patients, 14 each). All were treated with external beam radiotherapy, and toxicity assessed at the end of treatment and 10 to 14 days later (first recheck). All patients developed some acute radiation toxicity by the end of the course. However, there was no difference in the severity of toxicity between gross and microscopic disease in either site group at either time point. The only variable associated with an increased frequency of grade 2 or 3 toxicity at the first recheck was the use of prednisolone prior to radiotherapy (P = .05). No other factors were identified which were associated with increased toxicity. For the head group, the site of highest grade toxicity was mucosa or, if included in the field, nasal planum, which was often more severely affected than the mucosa. No significant late toxicity was identified. Two dogs developed acute haematemesis during the radiotherapy course, but both completed the course without further events.

Investigating Associations Between Proliferation Indices, C-kit, and Lymph Node Stage in Canine Mast Cell Tumors

Previous studies have evaluated cellular proliferation indices, KIT expression, and c-kit mutations to predict the clinical behavior of canine mast cell tumors (MCTs). The study purpose was to retrospectively compare mitotic index, argyrophilic nucleolar organizer regions (AgNORs)/nucleus, Ki-67 index, KIT labeling pattern, and internal tandem duplication mutations in c-KIT between stage I and stage II grade II MCTs. Medical records and tumor biopsy samples from dogs with Grade II MCTs with cytological or histopathological regional lymph node evaluation were included. Signalment, tumor location and stage, and presence of a recurrent versus de novo tumor were recorded. Mitotic index, AgNORs/nucleus, Ki-67, KIT staining pattern, and internal tandem duplication mutations in exon 11 of c-KIT were evaluated. Sixty-six tumors (51 stage I; 15 stage II) were included. Only AgNORs/nucleus and recurrent tumors were significantly associated with stage (odds ratio 2.8, 95% confidence interval [CI] 1.0–8.0, P = .049; odds ratio 8.8, 95% CI 1.1–69.5; P = .039). Receiver-operator characteristic analysis showed that the sensitivity and specificity of AgNORs/cell ≥ 1.87 were 93.3% and 27.4%, respectively, (area under the curve: 0.65) for predicting stage. Recurrent tumors and higher AgNORs/nucleus are associated with stage II grade II MCTs; however, an AgNOR cutoff value that reliably predicts lymph node metastasis was not determined.

Use of neutrophil to lymphocyte ratio for predicting histopathological grade of canine mast cell tumours

Canine mast cell tumours (MCTs) are variable in their biological behaviour and treatment decisions depend heavily on the histopathological grade. Biomarkers such as neutrophil to lymphocyte ratio (NLR) and albumin to globulin ratio are used to predict the biological behaviour of human neoplasms, but have not been widely studied in dogs. A retrospective analysis identified 62 cases of gross MCT (14 high-grade, 48 low-grade tumours). Median NLR was significantly different between high- and low-grade MCT and tumours at different locations. A multivariable model identified increasing NLR (OR 2.0) and age (OR 1.7) to be associated with an increased risk of high-grade MCT. Receiver operating characteristic curve analysis identified an NLR threshold value of 5.67 (sensitivity 85.7 per cent; specificity 54.2 per cent) for predicting a high-grade MCT. An NLR threshold of 5.67 could be useful alongside existing tools (appearance, location, etc.) to help to predict the grade of MCT. With further validation, this biomarker could be used to guide clinical decisions before obtaining a histopathological diagnosis.

Canine mast cell tumors: diagnosis, treatment, and prognosis

Mast cell tumors (MCTs) are the most common malignant skin cancer in dogs, and significant variability exists in their biological behavior. Most MCTs are cured with appropriate local therapy, but a subset shows malignant behavior with the potential to spread to lymph nodes, liver, spleen, and other areas and to thus become a systemic cancer. Because of this variable behavior, it is difficult to predict how any individual tumor is going to behave. The variability thus creates uncertainty in deciding what a particular dog’s prognosis is, whether staging tests to assess for metastasis are needed, and even what treatments will be necessary for best outcome. In addition to controversies over the potential for development of systemic disease, or diffuse metastasis, controversies also exist over what treatment is needed to best attain local control of these tumors. This article will briefly discuss the diagnosis of MCTs in dogs and will summarize the literature in regards to the controversial topics surrounding the more aggressive form of this disease, with recommendations made based on published studies.

The Prognostic Value of Lymph Node Metastasis with Grade 2 MCTs in Dogs: 55 Cases (2001–2010)

This study evaluates a series of dogs diagnosed with grade 2 cutaneous mast cell tumors (MCTs) with concurrent lymph node (LN) metastasis. All dogs had surgical excision of the primary tumor. The presence of metastasis was confirmed with either histopathology (n = 35) or cytology (n = 20). There was no significant difference in survival times (STs) between dogs with and without LN metastasis. Median survival time (MST) was not reached at 65.9 mo. LN palpation was a poor predictor of metastasis (sensitivity, .71; specificity, .54). Tumor location was the only prognostic factor for survival in this series of dogs. ST was greater for dogs that had removal of their metastatic LN. This study suggests that in dogs with grade 2 MCTs, outcome may not be affected by the presence of LN metastasis; however, removal of the metastatic LN may prolong survival.

The radiosensitizing effect of the aurora kinase inhibitors, ENMD-2076, on canine mast cell tumours in vitro

ENMD-2076 is an aurora kinase inhibitor that also has multi-target tyrosine kinase inhibitor properties. In this study, the mRNA and the protein expression of aurora-A and aurora-B were evaluated in three canine mast cell tumour cell lines. Dose-dependent cytotoxicity was seen in the cells treated, and it affected the cell cycle with cells in the G2/M phase being selectively killed. The cells were also evaluated for radiosensitivity with/without ENMD-2076, and radiosensitization was seen after 3 Gy and 6 Gy exposures with ENMD-2076 for 48 h. Protein expression of caspase-3 was gradually increased, and the expression intensity was highest at 24 h post irradiation in cells without ENMD-2076 treatment, which indicates that radiation exposure with ENMD-2076-induced cell death faster than radiation treatment alone. Our study results suggest the potential usefulness of treating canine mast cell tumours with aurora kinase inhibitors alone or in conjunction with radiation therapy.

Aggressive local therapy combined with systemic chemotherapy provides long-term control in grade II stage 2 canine mast cell tumour: 21 cases (1999-2012)

This retrospective case series evaluates the outcome of 21 dogs with grade II stage 2 mast cell tumour (MCT) treated with adequate local therapy and adjuvant systemic chemotherapy (prednisone, vinblastine and CCNU). The median survival for all dogs was 1359 days (range, 188-2340). Median disease-free interval was 2120 days (149-2325 days). Dogs treated with surgery and chemotherapy had shorter survival (median, 1103 days; 188-2010 days) than those that underwent surgery, radiation therapy and chemotherapy as part of their treatment (median, 2056 days; 300-2340 days). Two patients had local recurrence in the radiation field and four patients had de novo MCT. Distant metastasis was not observed in any dogs. The results of this study suggest that, in the presence of loco-regional lymph node metastasis in grade II MCT, the use of prednisone, vinblastine and CCNU after adequate local-regional therapy can provide a median survival in excess of 40 months.

Unilateral intraocular mastocytosis and anterior uveitis in a dog with subcutaneous mast cell tumors

A 9-year-old male castrated Scottish terrier was referred to the Radiation Oncology Service at the William R. Pritchard Veterinary Medical Teaching Hospital for palliative radiation therapy of an incompletely excised, recurrent subcutaneous mast cell tumor (MCT) located over the right scapula, and surgical removal of a perianal MCT. Three weeks after initial presentation and prior to the fifth radiation treatment, the patient was presented with cloudiness of the left eye of 3-7 days duration. Ophthalmic consultation revealed 3+ aqueous flare with a dependent, swirling component filling approximately one-third of the anterior chamber. Aqueocentesis was performed under general anesthesia. Cytology revealed mast cells with highly atypical morphology and considered most consistent with neoplasia. The patient died 7 months after pathologic diagnosis of MCT on the right shoulder and 2 months after the cytologic diagnosis of malignant mast cells in the left anterior chamber. To the authors' knowledge, this is the first report of intraocular involvement in a mammal with MCTs, described here as intraocular mastocytosis.

Survival times for canine intranasal sarcomas treated with radiation therapy: 86 cases (1996-2011)

Sarcomas comprise approximately one-third of canine intranasal tumors, however few veterinary studies have described survival times of dogs with histologic subtypes of sarcomas separately from other intranasal tumors. One objective of this study was to describe median survival times for dogs treated with radiation therapy for intranasal sarcomas. A second objective was to compare survival times for dogs treated with three radiation therapy protocols: daily-fractionated radiation therapy; Monday, Wednesday, and Friday fractionated radiation therapy; and palliative radiation therapy. Medical records were retrospectively reviewed for dogs that had been treated with radiation therapy for confirmed intranasal sarcoma. A total of 86 dogs met inclusion criteria. Overall median survival time for included dogs was 444 days. Median survival time for dogs with chondrosarcoma (n = 42) was 463 days, fibrosarcoma (n = 12) 379 days, osteosarcoma (n = 6) 624 days, and undifferentiated sarcoma (n = 22) 344 days. Dogs treated with daily-fractionated radiation therapy protocols; Monday, Wednesday and Friday fractionated radiation therapy protocols; and palliative radiation therapy protocols had median survival times of 641, 347, and 305 days, respectively. A significant difference in survival time was found for dogs receiving curative intent radiation therapy vs. palliative radiation therapy (P = 0.032). A significant difference in survival time was also found for dogs receiving daily-fractionated radiation therapy vs. Monday, Wednesday and Friday fractionated radiation therapy (P = 0.0134). Findings from this study support the use of curative intent radiation therapy for dogs with intranasal sarcoma. Future prospective, randomized trials are needed for confirmation of treatment benefits.

Radiotherapy-induced myelosuppression in dogs: 103 cases (2002-2006)

Definitive radiotherapy refers to delivery of large doses, typically 48-62 Gray, of ionizing radiation over several weeks using a daily or alternate-day fractionation schedule. The impact of definitive radiotherapy alone on haematopoiesis in tumour-bearing dogs is unknown. Medical records from 103 dogs receiving definitive (60) Cobalt teletherapy for cancer over a 5-year period were reviewed for signalment, tumour type and location, total radiotherapy dose and fractionation scheme. Complete blood count data were collected before, halfway through, and at the end of radiation treatment, and analysed for changes associated with patient variables. The results demonstrate significant reductions in haematocrit, total white blood cell count, neutrophils, eosinophils, monocytes, lymphocytes and platelets occurred during definitive radiotherapy but remained within laboratory reference intervals. These data are important for anticipation of toxicity associated with combinations of radiotherapy and chemotherapy in dogs but do not support the routine monitoring of haematology parameters during definitive radiotherapy.

Evaluation of Cisplatin as an electrochemotherapy agent for the treatment of incompletely excised mast cell tumors in dogs

BACKGROUND

Electrochemotherapy (ECT) couples the administration of anticancer drugs with the delivery of electric pulses that increase the drug uptake through the cell membranes, resulting in an improved efficacy.

HYPOTHESIS

To evaluate the tolerability and efficacy of cisplatin (CDDP) as an ECT agent to prevent recurrence of incompletely resected mast cell tumors (MCTs).

ANIMALS

Thirty-seven dogs.

METHODS

Prospective study recruiting dogs with incompletely excised MCTs as confirmed by surgeon and pathology reports. After debulking, the tumor bed and margins were infiltrated with CDDP, and then exposed to trains of biphasic electrical pulses under sedation. Five minutes after the injection of the chemotherapy agent, sequences of 8 biphasic pulses lasting 50 + 50 μs each, were delivered in bursts of 1,300 V/cm for sclerosed and of 800 V/cm for exposed lesions, with caliper or needle array electrodes, respectively. A second session was performed 1 or 2 weeks later based on clinical considerations.

RESULTS

The treatment was well tolerated with minimal adverse effects. Twenty-nine dogs had no evidence of recurrence over the 6-year study period, 6 had tumor recurrence, 1 died of multiple cutaneous MCTs, and 1 died of unrelated causes. The estimated median time to recurrence was 1,200 days. Recurrence was not observed among the long-term (> 1 year) treated dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

ECT with CDDP appears effective in the treatment of incompletely resected MCT in dogs and could be a useful addition to the current options based on its low cost, limited toxicity, and ease of administration.

Canine mast cell tumours: a review of the pathogenesis, clinical features, pathology and treatment

Mast cells (MCs) are well known for their neoplastic transformation in solitary and multiple cutaneous mast cell tumours (MCTs), as well as visceral and systemic mastocytosis. Dogs have a unique risk of developing cutaneous MCTs, and they account for 7% to 21% of all canine skin tumours. The aetiology of canine MCTs is unknown but is probably multifactorial. This article reviews up-to-date knowledge on the pathogenesis, the clinical presentation, the clinical prognostic factors, the diagnostic workup including clinical staging, cytological findings, histological findings and the various grading systems which have been evaluated based on morphology, the assessment of proliferation markers and other factors such as vessel density. Furthermore, detailed information about current treatment protocols for canine cutaneous MCTs is provided.

Adjuvant CCNU (Lomustine) and Prednisone Chemotherapy for Dogs With Incompletely Excised Grade 2 Mast Cell Tumors

The use of adjuvant 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU; lomustine) to treat incompletely excised canine mast cell tumors (MCTs) has not been evaluated. Medical records of 12 dogs with grade 2 MCT treated with incomplete surgical excision and adjuvant CCNU and prednisone chemotherapy were reviewed. Local recurrence rate, metastasis rate, and survival time were evaluated. None of the dogs developed local recurrence or regional/ distant metastases. Two dogs developed fatal liver failure. The 1- and 2-year progression-free rates of surviving dogs were 100% and 77%, respectively. Postoperative adjuvant CCNU appears to be a useful alternative to radiation therapy for incompletely excised canine cutaneous MCTs.

Veterinary radiation therapy: review and current state of the art

Veterinary radiation oncology became a recognized specialty in 1994. Radiation therapy is an important component of a multimodality approach to treating cancer in companion animals. It is important to understand the many aspects of radiation, including the equipment used in external beam radiation therapy, the basic mechanism of action of ionizing radiation, the results of irradiating various histopathological types of tumors, as well as the associated potential acute and late side effects of radiation. A comprehensive review of radiation therapy is timely and provides information for clients on cancers that may benefit from external beam radiation therapy.

Advances in the diagnosis and management of cutaneous mast cell tumours in dogs

Mast cell tumours are one of the most common tumours of the canine skin and have a reputation for being difficult to manage because of their variable clinical presentation, behaviour and response to treatment. This review of recent literature on canine mast cell tumours suggests that the majority of such tumours may not be as bad as their reputation suggests. Most grade I and grade II tumours can be managed successfully by good surgery. Recent literature also calls into question the utility of clinical staging systems and the value of assessing surgical margins for prognosis and highlights the paucity of well-conducted, case-controlled clinical trials in assessing the efficacy of medical management of high-risk tumours. In terms of more basic research, recent studies have implicated the stem cell factor receptor KIT as having a role in the aetiology of canine mast cell tumours and there appears to be an association between c-kit mutation and higher grade of tumour. This may offer a possible target for new therapeutic approaches.

Canine subcutaneous mast cell tumour: diagnosis and prognosis

The aim of this study was to characterize the pathology and clinical outcome of the subcutaneous variant of canine mast cell tumour. Fifty-three cases satisfying the inclusion criteria were selected from the pathology archive of the College of Veterinary Medicine, University of Tennessee. Referring veterinarians provided information on outcome. These dogs had a median age of 9 years (range 3-17 years). After characterizing tumours histologically, nuclear expression of proliferating cell nuclear antigen (PCNA) and Ki67 (MIB-1 clone) was determined immunohistochemically and mast cell origin was confirmed with c-Kit staining. Counts of argyrophilic nucleolar organizer regions (AgNOR) were determined by silver staining. Nuclear labelling was counted in 100 tumour cells. Margins were recorded as incomplete in 66% of dogs, and metastases occurred in 6% of dogs. The estimated minimum mean survival time from date of diagnosis was 1199 days, ranging from 55 to >1780 days. The median scores from immunohistochemical labelling were PCNA 0.05 and Ki67 0.03 per 100 tumour cells. The median score for AgNOR staining was 1.25 per 100 tumour cells. The patterns of c-Kit expression included membranous labelling in 20 tumours, stippled cytoplasmic labelling in 23 tumours and diffuse cytoplasmic labelling in 10 tumours. Age (r=-0.61, P=0.14) and AgNOR score (r=-0.58, P=0.17) had moderate, but non-significant, negative associations with survival. PCNA (r=-0.32, P=0.47), Ki67 (r=-0.22, P=0.64) and c-Kit immunolabelling was not associated with survival. The subcutaneous variant of canine mast cell tumour is distinct in having features of intermediate histological grade and extended mean survival times, suggesting a slightly better long-term prognosis than for higher grade dermal variants. Expression of nuclear proliferation markers is not associated with outcome.

Radiation Therapy for Incompletely Excised Grade II Canine Mast Cell Tumors

Forty-five dogs with incompletely excised grade II mast cell tumors were treated with radiation using a cobalt 60 teletherapy unit (15 fractions of 3.2 Gy for a total of 48 Gy). Twenty-four of the dogs underwent prophylactic regional lymph node irradiation. Three (6.7%) dogs had tumor recurrence, two (4.4%) dogs developed metastasis, and 14 (31%) dogs developed a second cutaneous mast cell tumor. No difference in overall survival rate was observed between the dogs receiving and not receiving prophylactic irradiation of the regional lymph node.

Outcome and prognostic factors following adjuvant prednisone/vinblastine chemotherapy for high-risk canine mast cell tumour: 61 cases

The medical records of 61 dogs with MCT at high risk for metastasis that were treated with prednisone and VBL following excision+/-radiation therapy were reviewed, and median disease-free interval (DFI), median overall survival time (OS) and prognostic factors assessed. Adverse effects, mostly mild, were noted in 26% of patients, usually after the first VBL dose. 6.5% experienced severe neutropenia. The DFI was 1305 days, and the OS was not reached, with 65% alive at 3 years. 100% of dogs with "high-risk" grade II MCT were alive at 3 years. The OS for dogs with grade III MCT was 1374 days. Histologic grade, location (mucous membrane vs. skin) and use of prophylactic nodal irradiation predicted outcome. Prednisone and VBL chemotherapy is well tolerated, and results in good outcomes following surgery in dogs with MCT at high risk for metastasis. High-grade and mucocutaneous tumors had a worse outcome, and the use of prophylactic nodal irradiation appeared to improve outcome in this group of dogs.

Impact of tumour depth, tumour location and multiple synchronous masses on the prognosis of canine cutaneous mast cell tumours

The goal of this study was to determine the significance of tumour depth, tumour location and multiple synchronous tumour masses for the prognostic evaluation of canine cutaneous mast cell tumours (MCTs). The study population consisted of 100 formalin-fixed, paraffin-embedded cutaneous MCTs that had been surgically removed from 100 dogs and submitted to the Diagnostic Center of Population and Animal Health at Michigan State University between 1998 and 2001. None of the dogs had received chemotherapy or radiation therapy. For each case the following data were obtained from the referring veterinarians: sex, breed, weight, age at diagnosis, diagnostics performed, adjunct medications given at the time of surgery, tumour location, number of tumour masses, tumour recurrence (development of MCTs at the surgical site), development of additional MCTs at distant sites (outside the surgical margins), tumour duration before removal, survival time and cause of death, if applicable. Tumour depth was determined through microscopic evaluation of 5 microm sections stained with haematoxylin and eosin. Based on univariable and multivariable survival analysis, dogs with multiple synchronous cutaneous MCTs at the time of diagnosis have a worse prognosis compared with dogs with single tumours. Additional treatment beyond surgical excision alone should be considered for these animals. Older dogs and Boxers with cutaneous MCTs were at higher risk to develop additional MCTs at distant sites (outside the surgical margins), and older and male dogs with cutaneous MCTs had significantly shorter survival times. Univariable analysis also determined that dogs with cutaneous MCTs located on the head and neck had an increased risk of additional MCT development at distant sites and that sterilized dogs with cutaneous MCTs had shorter survival times. However, these findings were not confirmed by multivariable analysis. Tumour depth was of no prognostic significance for dogs with cutaneous MCTs.

Tolerance of Cutaneous or Mucosal Flaps Placed into a Radiation Therapy Field in Dogs

OBJECTIVE

To determine the clinical outcome and factors affecting cutaneous or mucosal flaps in dogs treated with radiation therapy (RT).

STUDY DESIGN

Longitudinal clinical study.

ANIMALS

Twenty-six client-owned dogs.

METHODS

Dogs entered in the study had a flapping procedure and RT as part of their treatment. The sequence of flapping and RT included: (1) planned preoperative RT, (2) postoperative RT, and (3) flapping as a salvage procedure for management of complications or local tumor recurrence after RT. Flap complications were defined as necrosis, local infection, dehiscence, and ulceration. The risk and severity of flap complication were analyzed independently.

RESULTS

Twenty (77%) dogs had a complication; 6 dogs required an additional flapping procedure; and 4 dogs had an unresolved complication. Flapping procedures performed to correct a complication, or failure of RT, had a significantly greater risk for complication; however, postoperative RT decreased the severity of complication. A dose per fraction of 4 Gy compared with 3 Gy was prognostic for increased severity of complications, whereas the head and neck location was prognostic for decreased severity of complication.

CONCLUSIONS

Although morbidity was substantial, cutaneous or mucosal flaps were used successfully in an RT field in 85% of the dogs. Flaps that were part of the planned therapy as opposed to those used to correct a complication or failure of RT had a better clinical outcome.

CLINICAL RELEVANCE

Cutaneous or mucosal flaps can be part of the treatment of dogs with tumor when adjuvant or neoadjuvant RT is to be used.

Outcome of dogs with mast cell tumors in the inguinal or perineal region versus other cutaneous locations: 124 cases (1990?2001)

OBJECTIVE

To compare clinical outcome of dogs with cutaneous mast cell tumors (MCTs) in the inguinal or perineal region with outcome for dogs with MCTs in other cutaneous locations.

DESIGN

Retrospective study.

ANIMALS

37 dogs with MCTs in the inguinal or perineal region and 87 dogs with MCTs in other cutaneous locations.

PROCEDURE

Information obtained from the medical records included sex, breed, age, histologic grade of all tumors, number and location of all tumors, tumor size (ie, diameter of the tumor), completeness of surgical excision, treatments administered in addition to surgery, and outcome. In all dogs, the primary treatment consisted of surgical excision.

RESULTS

Disease-free interval and survival time for dogs with MCTs in the inguinal or perineal region were not significantly different from values for dogs with MCTs in other cutaneous locations. Dogs with incompletely excised tumors, dogs with grade III tumors, and dogs that received systemic treatment were 2, 2.5, and 4 times as likely, respectively, to have a relapse. Factors significantly associated with a shorter survival time were age > 8 years, metastatic disease at the time of initial diagnosis, and tumor relapse.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of the present study suggest that dogs with MCTs in the inguinal or perineal region do not have a worse prognosis in regard to disease-free interval or survival time than do dogs with MCTs in other cutaneous locations. Treatment recommendations for dogs with cutaneous MCTs should be based on confirmed predictors of biological behavior, such as histologic grade and clinical stage.

Partial Foot Amputation in 11 Dogs

Eleven dogs with malignant tumors of the digits and feet were treated with partial foot amputation. Partial foot amputation involved amputation of one or both central weight-bearing digits. Lameness occurred in all dogs but resolved in eight dogs at a median of 37 days postoperatively. In the remaining three dogs, lameness improved but did not resolve. Tumor control was excellent, with no evidence of local recurrence in 10 dogs. One dog underwent limb amputation. Based on these results, partial foot amputation may be recommended in the management of malignant tumors of the canine foot in which more than one digit must be amputated to achieve adequate surgical margins.

Mast cells and canine mast cell tumours. A review

This article reviews the literature on mast cells and tumours derived from mast cells in the dog. Mast cells play a central role in inflammatory and immune reactions. Mast cells, normal and neoplastic, contain and release important biologically active substances: heparin, histamine, eosinophilic chemotactic factor and proteolytic enzymes. Mast cell tumours occur in the dog, particularly in the boxer and related breeds, in the skin and less frequently in the intestines. Cytology usually provides an accurate diagnosis, but histological examination adds further information concerning the histologic grade and the completeness of surgical therapy. Cutaneous mast cell tumours should be regarded as potentially malignant and therefore be removed widely (3 cm. margin). Local recurrence, regional and distant metastases together with paraneoplastic disorders may cause the death of the pet. Histologic grading (2 or 3 grades) and clinical staging together with kinetic parameters and breed (boxers have relatively benign tumours) are important prognostic parameters. Based on prognostic criteria, surgical treatment should be completed with adjuvant radiotherapy, corticosteroids and eventually with combined chemotherapy. A novel, promising therapy is the application of the receptor kinase inhibitor. The study of the pathogenesis of mast cell tumours received new impetus by the finding of mutations, deletions and duplications, in exons 11 and 12 of the C-kit oncogene. Further study of physiological and oncological aspects of mast cells are favoured by the availability of mast cells isolated from spontaneous mast cell tumours and of cultured cell lines.

Prognostic factors for survival of dogs with inguinal and perineal mast cell tumors treated surgically with or without adjunctive treatment: 68 cases (1994-2002)

OBJECTIVE

To determine the prognostic factors for survival and tumor recurrence in dogs with cutaneous mast cell tumors (MCTs) in the perineal and inguinal regions treated surgically with or without adjunctive radiation therapy, chemotherapy, or both.

DESIGN

Retrospective study.

ANIMALS

68 dogs.

PROCEDURE

Medical records of dogs with histologically confirmed MCTs in the perineal region, inguinal region, or both treated surgically with or without adjunctive radiation therapy, chemotherapy, or both were reviewed.

RESULTS

Mean tumor-free interval was 1,635 days (median not reached), and 1- and 2-year tumor-free rates were 79% and 71%, respectively. Median survival time was 1,111 days (mean, 1,223 days), and 1- and 2-year survival rates were 79% and 61%, respectively. Factors that negatively influenced survival time were age at diagnosis, tumor recurrence, and treatment with lomustine.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that dogs with MCTs in the inguinal and perineal regions, if appropriately treated, may have survival times and tumor-free intervals similar to dogs with MCTs in other locations.

Iridium-192 Interstitial Brachytherapy as Adjunctive Treatment for Canine Cutaneous Mast Cell Tumors

Eleven dogs with cutaneous mast cell tumors (MCTs) were treated with surgery and iridium-192 (192Ir) interstitial brachytherapy. Minimum tumor doses ranged from 47.2 to 63.3 Gy. Treated tumors were classified as grade II (n=7) or III (n=4). Five dogs had recurrences with a median progression-free interval of 1391 days, and six dogs had no recurrence at a median follow-up time of 942 days. Acute adverse effects were well tolerated, and late effects were mild. One dog developed a second tumor of a different cell type in the radiation treatment field.

Vinblastine and Prednisolone as Adjunctive Therapy for Canine Cutaneous Mast Cell Tumors

Twenty-seven dogs with inadequately excised, cutaneous mast cell tumors (MCT; 20 residual microscopic disease, seven marginal excision) were treated with a vinblastine and prednisolone chemotherapeutic protocol. Twenty dogs were available for follow-up examination after 12 months. One dog suffered local recurrence of the tumor, four dogs developed new cutaneous tumors, and one dog had both events. Fourteen dogs were free of MCT. There was no confirmed tumor-related mortality. Although toxicity from the chemotherapy was generally mild, one dog died of sepsis during treatment.

Efficacy of radiation therapy for incompletely resected grade-III mast cell tumors in dogs: 31 cases (1987–1998)

OBJECTIVE

To determine the efficacy (durations of remission and survival) of an alternating-day radiation protocol for incompletely excised histologic grade-III solitary mast cell tumors (MCTs) in dogs.

DESIGN

Retrospective study.

ANIMALS

31 dogs.

PROCEDURE

Radiation (52 Gy in an 18-fraction alternating-day protocol) was delivered to an area bordered by margins > or = 3 cm around the surgical scar and to the associated local-regional lymph nodes. Dogs were not given chemotherapeutic agents concurrently or after radiation. Information on signalment, duration of remission, and survival time was obtained from medical records.

RESULTS

Median and mean durations of remission were 27.7 and 17.0 months, respectively (range, 1 to 47 months). Median and mean durations of survival were 28 and 20 months, respectively (range, 3 to 52 months). Dogs with tumors located on the skin of the pinna, perineum, and prepuce had a median duration of remission greater than dogs with tumors located at other sites (27.7 and 14.4 months, respectively). Dogs with tumors < or = 3 cm in maximum diameter before surgery survived longer than dogs with tumors > 3 cm (31 and 24 months, respectively). The remission rate was 65% and survival rate was 71% at 1 year after treatment. Sixteen dogs that were euthanatized had complications associated with local-regional tumor progression. Systemic metastases to liver, spleen, intestine, and bone marrow were detected in 1 dog.

CONCLUSIONS AND CLINICAL RELEVANCE

Without further treatment, incompletely excised grade-III mast cell tumors have high local-regional recurrence; local-regional treatment with radiation may effectively be used to manage many such tumors.

Biologic behavior and prognostic factors for mast cell tumors of the canine muzzle: 24 cases (1990-2001)

The medical records of 24 dogs with histologically confirmed mast cell tumors (MCT) of the muzzle were retrospectively evaluated to determine their biologic behavior and prognostic factors. Information on signalment, tumor grade and stage, treatment methods, and pattern of and time to failure and death was obtained from the medical record. Twenty-three dogs were treated with combinations of radiotherapy, surgery, and chemotherapy; 1 dog received no treatment. There were 2 Grade 1, 15 Grade 11, and 7 Grade III tumors. Tumors were stage 0 (n = 8), stage 1 (5), stage 2 (6), stage 3 (4), and stage 4 (1). Mean and median survival times of treated dogs were 36 and 30 months, respectively. Prognostic factors affecting survival time included tumor grade and presence of metastasis at diagnosis. Dogs with Grade I and II tumors survived longer than dogs with Grade III tumors. Variables, including sex, age, gross versus microscopic disease, and treatment type were not found to affect survival. Local control rate was 75% at 1 year and 50% at 3 years. Tumor grade was the only variable found to affect local control. Dogs with Grade I tumors had longer disease-free intervals than those with Grade II tumors, and dogs with Grade II tumors had longer disease-free intervals than dogs with Grade III tumors. Eight of 9 dogs dying of MCT had local or regional disease progression. Muzzle MCT a rebiologically aggressive tumors with higher regional metastatic rates than previously reported for MCT in other sites.