Association of breed and histopathological grade in canine mast cell tumours

The aim of this study was to evaluate the relationship between breed and the histopathological grade of canine mast cell tumours (MCTs). A retrospective survey of pathology data of 9375 histopathologically confirmed diagnoses of cutaneous MCTs in the US was evaluated in the context of breed prevalence in over two million registered purebred dogs. Association of histopathological grade with breed, age, sex and spay/neuter status was assessed. The data indicate that the proportion of high‐grade tumours increases with advancing age, and that male and intact dogs have increased odds of developing high‐grade tumours. A significant difference in the proportion of high‐grade tumours between breeds was detected. The Pug was at significantly increased risk of developing low/intermediate‐grade tumours, but not high‐grade tumours, resulting in preponderance of less aggressive MCTs in this breed. The results of this study suggest a genetic association for the development of high‐grade MCTs.     

Masitinib mesylate for metastatic and non‐resectable canine cutaneous mast cell tumours

Masitinib mesylate is a tyrosine kinase inhibitor approved for the treatment of gross, non‐metastatic grade II and III canine mast cell tumours (MCTs). This study evaluated the use of masitinib as a frontline and rescue agent for metastatic and non‐metastatic canine MCTs. Identification of toxicities and prognostic factors in these dogs was of secondary interest. Twenty‐six dogs were included in this study. The overall response rate to masitinib was 50%. The median survival time for dogs that responded to masitinib was 630 days versus 137 days for dogs that did not respond (P = 0.0033). Toxicity was recorded in 61.5% of treated dogs, but the majority of adverse events were mild and self‐limiting. Response to masitinib, not tumour grade, stage or location, was the most significant prognostic factor for survival in dogs with MCTs.     

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.     

Evaluation of the global DNA methylation in canine mast cell tumour samples by immunostaining of 5‐methyl cytosine

Cutaneous mast cell tumours (MCT) are the most common skin tumour in dogs, and to our knowledge, there are no previous studies regarding the global methylation of these tumours. DNA hypomethylation and hypermethylation have been described in several tumours and both mechanisms can lead to carcinogenesis. The purpose of this study was to evaluate the global DNA methylation in canine MCT. A total of 48 MCT samples were classified in grades 1, 2 and 3 or high‐grade or low‐grade. Monoclonal antibodies were used for the immunohistochemical detection of the 5‐methylcytosine. The immunostained nuclei were classified in strong, weak or negative pattern, and these were quantified in five distinct microscopic fields (40× objective) in each slide. The results showed that global DNA hypomethylation was predominant in grade 3, high‐grade, less differentiated MCT. These epigenetic changes in neoplastic mast cells warrant further detailed investigation aiming the establishment of tumour epigenetic therapies.     

Diagnostic accuracy of pre‐treatment biopsy for grading cutaneous mast cell tumours in dogs

Mast cell tumours (MCTs) are common tumours of the canine skin, and are estimated to represent up to 20% of all skin tumours in dogs. Tumour grade has a major impact on the incidence of local recurrence and metastatic potential. In addition to helping the clinician with surgical planning, knowledge of the tumour grade also assists in proper prognostication and client education. For pre‐treatment biopsies to be useful, there must exist a high level of correlation between the histopathological grade obtained from the pre‐treatment biopsy and the actual histopathological grade from the excisional biopsy. The aim of this study was to determine concordance of tumour grade between various biopsy techniques (wedge, punch, needle core) and the “gold standard” excisional biopsy method. We found an overall concordance rate of 96% based on the Patnaik grading system, and an overall concordance rate of 92% based on the Kiupel grading system. The accuracy of the various biopsy techniques (wedge, punch and needle core) when compared with excisional biopsy was 92%, 100% and 100%, respectively, based on the Patnaik grading system, and 90%, 95% and 100%, respectively, based on the Kiupel grading system. Of the cases with discordant results, the pre‐treatment biopsies tended to underestimate the grade of the tumour. Based on these results, we conclude that pre‐treatment biopsies are sufficiently accurate for differentiating low‐grade from high‐grade MCTs, regardless of biopsy technique or tumour location.     

Immunohistochemical evaluation of prostaglandin E2 and vascular endothelial growth factor in canine cutaneous mast cell tumours

Vascular endothelial growth factor (VEGF) and prostaglandin E2 (PGE-2) appear to play a critical role in tumour neovascularization. In this study, we have investigated the expression of VEGF and PGE-2 in 53 canine cutaneous mast cell tumours (MCTs). Immunohistochemistry of tissue sections revealed that VEGF and PGE-2 were expressed in all mast cell tumours studied. When the expression patterns of VEGF and PGE-2 were compared with tumour grade according to Patnaik criteria, the only significant correlation observed was between PGE-2 staining intensity and tumour pathological grade, with grade II and III tumours having higher PGE-2 staining, both in intensity and percentage of cells stained, than grade I tumours ( P < 0.05).     

In situ c‐KIT mRNA quantification of canine cutaneous mast cell tumours and its relationship to prognostic factors

Cutaneous mast cell tumours (MCTs) are the most frequent malignant skin tumours in dogs. Mutations in the c‐KIT proto‐oncogene are correlated with the pathogenesis and aggressiveness of MCTs. To date, studies have focused on c‐KIT mutations and KIT protein localization, with a general lack of mRNA‐level analyses. In this study, c‐KIT mRNA expression was investigated in canine MCTs by RNA in situ hybridization (RNA‐ISH). Furthermore, we evaluated associations between c‐KIT mRNA expression and the histological grade, KIT immunohistochemical staining pattern and other clinicopathological parameters. c‐KIT mRNA expression was observed in all MCT samples, appearing as clusters of dots in the cytoplasm of neoplastic cells. A significant correlation was detected between c‐KIT mRNA expression (quantified according to the H‐score and the percentage of positive cells) and the histological grade (determined using two‐and three‐tier grading systems; P < .05). We also found a significant positive correlation (all P < .05) between c‐KIT mRNA expression and the proliferation indices (mitotic index, Ki‐67, and Ag67). However, no significant associations with c‐KIT expression from RNA‐ISH were found with respect to different KIT staining patterns. Overall, these results demonstrate that c‐KIT mRNA expression might be an additional tool for measuring the c‐KIT status in canine cutaneous MCTs and could serve as a potential prognostic factor. Further studies should evaluate the prognostic significance of c‐KIT mRNA expression in a large and uniform cohort of canine MCTs.     

Evaluation of histological grade and histologically tumour‐free margins as predictors of local recurrence in completely excised canine mast cell tumours

Completeness of mast cell tumour (MCT) excision is determined by assessment of histologically tumour‐free margins (HTFM). The HTFM width necessary to prevent local recurrence (LR), recognized as histologic safety margin (HSM) in human oncology, has not been defined. We hypothesized that HTFM width would correlate with risk for LR and high‐grade tumours would require wider HTFM than low‐grade tumours. Records of dogs with completely excised MCTs were included. Signalment, two‐tier tumour grade, tumour size, HTFM width, recurrence and therapy data was collected. High‐grade (n = 39) tumours were more likely to recur than low‐grade (n = 51) tumours (35.9% versus 3.9%), P < 0.0001, with no association between HTFM width and LR. Twenty‐nine percent of low‐grade tumours had HTFM less than 3 mm; none recurred. Narrow (≤3 mm) histologic margins are likely adequate to prevent LR of low‐grade tumours. High‐grade tumours have significant risk of LR regardless of HTFM width.     

Evaluation of prognostic indicators in dogs with multiple,simultaneously occurring cutaneous mast cell tumours: 63 cases

Sixty‐three dogs with multiple contemporaneous cutaneous mast cell tumours (MCTs) were identified. The aim of this study was to determine the significance of breed, concurrent dermatological condition; number of cutaneous MCTs, size, location, histological grade and mitotic index; completeness of excision (complete, close or incomplete); local recurrence, metastasis and adjuvant therapy for the prognostic evaluation of dogs with a unique disease presentation of multiple, simultaneously occurring cutaneous MCTs. On the basis of multivariable survival analysis, dogs with one recorded grade 3 MCT had shorter progression‐free survival (PFS) times (18.7 versus 2.2 months) and median survival times (MSTs) (24 versus 3 months). Dogs treated with adjuvant vinblastine/lomustine had a 16 times increased risk of dying. MSTs were found to be significantly longer in dogs with one recorded MCT on an extremity. For all dogs, the PFS (range 14–1835 days) and MSTs (range 28–1835 days) were not reached.     

COX‐2 and c‐kit expression in canine gliomas

Gliomas are among the most common primary neural tumours of dogs. Cyclooxygenase‐2 (COX‐2) and c‐kit overexpression are associated with increased aggressiveness of gliomas and decreased survival in human beings. COX‐2 is the inducible form of cyclooxygenase, which catalyzes prostaglandin formation and may increase tumour proliferation and angiogenesis. C‐kit is a tyrosine kinase receptor involved in normal cell physiology; c‐kit is upregulated in some canine tumours. In this retrospective study, 20 canine gliomas were identified: 11 (55%) oligodendrogliomas, including 1 anaplastic variant; 1 (5%) oligoastrocytoma; and 8 (40%) astrocytomas, of which 2 were glioblastoma multiforme. None of the gliomas expressed COX‐2. None of the gliomas were immunoreactive for c‐kit, although all three high‐grade tumours had intramural vascular expression. Consequently, COX‐2 inhibitors would likely be ineffective against canine gliomas. C‐kit inhibitors may have an anti‐angiogenic effect in high‐grade gliomas, but would likely be ineffective in low‐ and medium‐grade tumours.     

High lysyl oxidase expression is an indicator of poor prognosis in dogs with cutaneous mast cell tumours

Mast cell tumour (MCT) is one of the most frequent skin tumours in dogs. Due to their unpredictable biological behaviour, MCTs often cause several therapeutic frustrations, leading to investigation regarding prognostic markers. Lysyl oxidase (LOX) is an enzyme that promotes extracellular matrix stability and contributes to cell migration, angiogenesis and epithelial-mesenchymal transition. Its expression positively correlates with poor prognoses in several human and canine mammary cancers. The aim of this study was to characterise the immunohistochemical expression of LOX in MCT samples and compare it with histological grading and post-surgical survival. Twenty-six tumours were submitted to immunohistochemistry for LOX expression evaluation. All samples were positive for LOX, with variable percentages of cytoplasmic and nuclear positivity. Cytoplasmic positivity was significantly higher in high-grade MCTs (P = .0297). Our results indicate that high expression of cytoplasmic LOX in neoplastic mast cells is an indicator of poor prognosis for canine cutaneous MCTs.     

Cytological grading of canine cutaneous mast cell tumours

A cytological grading for mast cell tumours (MCTs) would be highly desirable, allowing to select the most appropriate therapeutic intervention prior to surgery. This study evaluates the applicability on fine‐needle aspirations (FNAs) of the novel Kiupel grading system, based on number of mitoses, multinucleated cells, bizarre nuclei and presence of karyomegaly. Fifty consecutive cases with pre‐operative cytological diagnosis were included. In cytological specimens, approximately 1000 cells were evaluated, and the histological grade was assessed on the corresponding resected specimens. On cytology, the above parameters were significantly different between histologically low‐grade and high‐grade tumours (P < 0.001). The cytograding correctly predicted the histological grade in 47 cases (accuracy, 94%; sensitivity, 84.6%; specificity, 97.3%). Two high‐grade MCTs (4%) were not detected on cytology. The cytograding can provide helpful insights to assist clinical decisions in most cases. However, the risk of underestimation in a minority of patients represents a limit to the overall utility of the technique.     

Concentration of extracellular vesicles isolated from blood relative to the clinical pathological status of dogs with mast cell tumours

Extracellular vesicles (EVs) are membrane‐enclosed fragments shed from all cell types, including tumour cells. EVs contain a wide range of proteins, biolipids and genetic material derived from mother cells and therefore may be potential biomarkers for tumour diagnosis, disease progression and treatment success. We studied the effect of canine mast cell tumours (MCTs) on EV concentrations in blood isolates in association with MCT's histological grade, Ki‐67 proliferative index, KIT‐staining pattern and number of PLT. The average EV concentration in blood isolates from nine dogs with MCTs was considerably higher than that in blood from eight healthy dogs. But there were no statistically significant differences in EVs concentration in the population of dogs with MCT according to a different histological grade of malignancy (Patnaik, Kiupel), KIT‐staining pattern and Ki‐67 proliferation index. The results show that these variables statistically do not significantly predicted EV concentrations in blood isolates (P > .05), except the KIT‐staining pattern I which added statistically significantly to the prediction (P < .05). The results confirmed the impact of neoplasms on the morphological changes to cell membranes, which result in greater vesiculability and higher EV concentrations.     

Canine parvovirus in Australia: The role of socio-economic factors in disease clusters

To identify clusters of canine parvoviral related disease occurring in Australia during 2010 and investigate the role of socio-economic factors contributing to these clusters, reported cases of canine parvovirus were extracted from an on-line disease surveillance system. Reported residential postcode was used to locate cases, and clusters were identified using a scan statistic. Cases included in clusters were compared to those not included in such clusters with respect to human socioeconomic factors (postcode area relative socioeconomic disadvantage, economic resources, education and occupation) and dog factors (neuter status, breed, age, gender, vaccination status). During 2010, there were 1187 cases of canine parvovirus reported. Nineteen significant (P<0.05) disease clusters were identified, most commonly located in New South Wales. Eleven (58%) clusters occurred between April and July, and the average cluster length was 5.7days. All clusters occurred in postcodes with a significantly (P<0.05) greater level of relative socioeconomic disadvantage and a lower rank in education and occupation, and it was noted that clustered cases were less likely to have been neutered (P=0.004). No significant difference (P>0.05) was found between cases reported from cluster postcodes and those not within clusters for dog age, gender, breed or vaccination status (although the latter needs to be interpreted with caution, since vaccination was absent in most of the cases). Further research is required to investigate the apparent association between indicators of poor socioeconomic status and clusters of reported canine parvovirus diseases; however these initial findings may be useful for developing geographically- and temporally-targeted prevention and disease control programs.     

PCNA and grade in 13 canine oral squamous cell carcinomas: association with prognosis

This study evaluated the prognosis factors of age, tumour size, anatomic location, histological grade and proliferating cell nuclear antigen (PCNA) expression in 13 dogs with oral squamous cell carcinoma (OSCC) with bone invasion and without signs of lymph node or distant metastasis. All animals were treated with radical excision performed with at least 1 cm margin, based on computed tomography images. In the 2‐year follow‐up, median disease‐free survival was 138 days for dogs with grade 3 tumours and was not reached for those with grade 2 tumours. Grade 3 tumours and PCNA labelling index ≥65% were related with a shorter disease‐free survival time and consequently poor prognosis (p = 0.003 and p = 0.034, respectively). Mean PCNA labelling index was significantly higher in recurrent cases (p = 0.011). Histological grade and PCNA expression may be important prognosis factors in canine OSCC.     

TSLC1 tumour-suppressor gene expression in canine mast cell tumours

Tumour suppressor in lung cancer-1 (TSLC1) is a tumour-suppressor gene coding for an adhesion molecule that is expressed by mast cells. Reduced TSLC1 expression is associated with a poor prognosis in several human tumours, and this study sought to investigate if TSLC1 expression could be used to predict outcome in dogs with mast cell tumours (MCTs). Sections of MCTs of different tumour grades from 45 dogs (Group 1) were immunohistochemically assessed for TSLC1 and Ki67 expression. In addition, 35 intermediate-grade MCTs (Group 2) from dogs with known clinical follow-up were immunohistochemically stained for TSLC1 and Ki67. The TSLC1 staining intensity was found to strongly inversely correlate with tumour grade for Group 1 (P = 0.002857). For Group 2 there was a trend towards dogs with lower TSLC1 scores being more likely to die from MCT-related disease (P = 0.058). The intensity of TSLC1 staining inversely correlated with Ki67 expression for both groups.     

Influence of E‐cadherin genetic variation in canine mammary tumour risk,clinicopathological features and prognosis

E‐cadherin is a cell adhesion molecule that participates in several cellular processes that guarantee the maintenance of structural and functional integrity of epithelial tissues. E‐cadherin plays an important role in mammary carcinogenesis, and various studies have demonstrated the effect of CDH1 genetic variation in risk, progression and biological behaviour of human breast cancer. Although there are some recognized genetic variations in canine CDH1 gene, their influence in canine mammary tumour development and progression has not been previously evaluated. In this study, we aim to assess the influence of CDH1 SNPs rs850805755, rs852280880 and rs852639930 in the risk, clinicopathological features and clinical outcome of canine mammary tumours. A case‐control study was conducted involving 206 bitches with mammary tumours and 161 bitches free of mammary neoplasia. CDH1 SNPs rs850805755 and rs852280880 were associated with a decreased risk and a later onset of mammary tumour development. Furthermore, these SNPs were related to the development of small size carcinomas, of low histological grade and low nuclear pleomorphism. SNP rs852639930 was associated with the development of small size tumours with a non‐infiltrative, non‐invasive growth pattern. Data from the present investigation demonstrate that these CDH1 genetic variants could have a protective role in canine mammary tumours, by being associated with low risk of tumour development, delayed onset of the disease and less aggressive clinicopathological features.     

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.     

The treatment of canine mast cell tumours with electrochemotherapy with or without surgical excision

To describe the results of electrochemotherapy (ECT) in dogs with mast cell tumours (MCTs) either as first line therapy or as an adjuvant to surgery. The treatment combines administration of low dose chemotherapeutic drugs with the application of microsecond electric pulses, which cause the temporary permeabilization and increased porosity of the tumour cell membranes. The design of this study is a retrospective case series. A total of 51 dogs with MCTs were included and classified according to ECT procedure into 4 groups (ECT only, 15 cases, intra‐surgery ECT, 11, ECT Adjuvant to surgery, 14, Surgery followed by ECT, 11). The four groups (staged with location, size and grade) were evaluated to assess complete or partial remission, disease free interval, overall survival time and local toxicity. In this case series, Boxers, mixed breed and Labrador Retrievers, male dogs, between 4 and 9 years old were more represented. MCTs were predominantly grade 2 (Patnaik) and T stage 0–1, I‐1 (World Health Organization). Treated lesions were most commonly identified on the hindlimb and head where curative surgery would involve cosmetic or functional compromise. The intra‐surgery group of dogs showed the best disease free interval with Kaplan–Meyer analysis. Local toxicity induced by ECT ranged mostly from 1 to 4 in a 5‐point arbitrary scale with 0 – no toxicity to 5 – highest toxicity. In this study, ECT can be applied successfully as an exclusive therapy in smaller MCTs as an alternative to surgery. ECT can be combined with surgery either intra‐operatively or post operatively for larger lesions without significant toxicity.