A 2-tiered histologic grading scheme for canine cutaneous mast cell tumors (MCTs) is based on morphologic characteristics of neoplastic cells, including karyomegaly, multinucleation, nuclear pleomorphism, and mitotic figures. Aspirates from MCTs may provide the same information more quickly, inexpensively, and less invasively. This study used these criteria to develop a cytologic grading scheme for canine MCTs to predict outcome. Three anatomic pathologists graded histologic samples from 152 canine MCTs. Three clinical pathologists evaluated aspirates from these masses using similar criteria. A cytologic grading scheme was created based on correlation with histologic grade and evaluated with a kappa statistic. Survival was evaluated with Kaplan-Meier survival curves. Cox proportional hazards regression was used to estimate hazard ratios for tumor grades and individual grading components. Simple logistic regression tested for relationships between risk factors and mortality. The cytologic grading scheme that best correlated with histology (kappa = 0.725 ± 0.085) classified a tumor as high grade if it was poorly granulated or had at least 2 of 4 findings: mitotic figures, binucleated or multinucleated cells, nuclear pleomorphism, or >50% anisokaryosis. The cytologic grading scheme had 88% sensitivity and 94% specificity relative to histologic grading. Dogs with histologic and cytologic high grade MCTs were 39 times and 25 times more likely to die within the 2-year follow-up period, respectively, than dogs with low grade MCTs. High tumor grade was associated with increased probability of additional tumors or tumor regrowth. This study concluded that cytologic grade is a useful predictor for treatment planning and prognostication.
Abstract. Ten veterinary pathologists independently assigned histologic grades to the same 60 canine cutaneous mast cell tumors using the Patnaik classifications. The degree of agreement in grading among the pathologists was compared with the degree of agreement among the same pathologists in a previous study, in which each pathologist used the reference for grading that he/she uses routinely. Mean agreement improved significantly from 50.3% to 62.1% with uniform use of the Patnaik classifications (P ϭ 0.00001), suggesting that there is value in uniform application of a single grading scheme for canine cutaneous mast cell tumors. Agreement among pathologists was still not 100%, suggesting that a more objective grading scheme should be developed and that other histologic indicators of prognosis should be investigated.Key words: Dogs; grade; histopathology; mastocytoma.Mast cell tumors (MCTs) are the most common cutaneous tumors of the dog. 13 These tumors vary widely in their behavior, from nearly benign to highly invasive and metastatic. It has been recognized for more than 30 years that histologic grading is prognostic for the behavior of canine cutaneous MCTs. 3,6,10 The 2 most widely recognized grading systems classify MCTs into 3 grades based on histologic characteristics, including cellularity, cell morphology, invasiveness, mitotic activity, and stromal reaction. 3,10 Both grading systems correlate with the survival rate of canine patients with MCTs and histologic grade is the most important factor in determining the staging tests and adjunctive therapy that will be recommended for a dog with a cutaneous MCT. 9,13 Because of the importance of histologic grade in prognosis and decision making in the therapeutic management of dogs with MCTs, it is essential that veterinarians understand the variability among pathologists in assigning grades to MCTs. In a previous study, it was demonstrated that there was significant variation in the histologic grades assigned to the same 60 canine cutaneous MCTs by 10 veterinary pathologists at 1 institution. 8 Because variation in histologic grading was significantly associated with the use of different references describing grading systems, it was hypothesized that if all pathologists utilized the same reference for grading, there would be improved agreement in the grades as- signed to canine cutaneous MCTs. The objective of this study was to determine whether variation among veterinary pathologists in the histologic grading of canine cutaneous MCTs could be eliminated by uniform use of a single grading scheme.Ten veterinary pathologists independently graded the same 60 canine cutaneous MCTs as grade I, II, or III using the Patnaik classifications (Table 1). 10 These were the same 10 veterinary pathologists who participated in the previous study to evaluate variation among pathologists in histologic grading of canine cutaneous MCTs. 8 Four of these pathologists were from the University of Georgia College of Veterinary Medicine (UGA-CVM) Department of Pathology, 5 were from...
Abstract. Ten veterinary pathologists at 1 veterinary institution independently assigned histologic grades to the same 60 canine cutaneous mast cell tumors (MCTs). There was significant variation among pathologists in grading the MCTs (P Ͻ 0.001). The probability of assigning a low grade was significantly higher for the pathologists in this study who use a published reference for histologic grading of canine cutaneous MCTs that allows subcutaneous MCTs or MCTs with mitotic figures to be included in the low-grade category (P Ͻ 0.0001 and P Ͻ 0.0001, respectively).Key words: Dog; grade; histopathology; mastocytoma.Mast cell tumors (MCT) are the most common cutaneous neoplasm of the dog. 10 These tumors vary widely in their behavior from nearly benign to highly invasive and metastatic. It has been recognized for more than 30 years that histologic grading is prognostic for the behavior of canine cutaneous MCTs. 2,4,7 The 2 most widely recognized grading systems classify MCTs into 3 grades based on histologic characteristics that include: cellularity, cell morphology, invasiveness, mitotic activity, and stromal reaction. 2,7 Both grading systems correlate with the survival rate of canine patients with MCT. Well-differentiated, low-grade (Patnaik Grade I, Bostock Grade 3) MCTs are generally benign in behavior and are usually cured by surgical excision. Poorly differentiated, high-grade (Patnaik Grade III, Bostock Grade 1) MCTs are generally locally invasive, more likely to metastasize, and associated with a poor survival rate. The histologic appearances and clinical courses of intermediategrade MCTs range between those of high-and low-grade MCTs.
Abstract. Although cytauxzoonosis has historically been nearly 100% fatal in domestic cats, increasing number of reports of infected cats that demonstrate less-severe disease suggest the existence of different strains of Cytauxzoon felis. To test this hypothesis, the genetic variability of C. felis was examined in blood samples from naturally infected domestic cats from Arkansas and Georgia by using the first and second ribosomal internal transcribed spacer regions (ITS1, ITS2) as markers to assess genotypic variability. In addition, the clinical outcome of infection (survival vs. fatal disease) was analyzed. Within the C. felis ITS1 region, there were a total of 8 single nucleotide polymorphisms (SNP) and a single nucleotide insertion. Within the ITS2 region, there were a total of 4 SNPs and a single 40 base pair insertion. When taken together, the ITS1 and ITS2 sequence data defined a total of 11 different sequences and 3 unique genotypes. One unique ITS1-ITS2 genotype was detected in samples submitted exclusively from Arkansas, and a second unique genotype was submitted exclusively from Georgia. There was a significant association between infection with C. felis that contained particular ITS genotypes and survival of the infected domestic cat. The identification of unique C. felis genotypes obtained from different geographic areas and the association of particular ITS genotypes with the outcome of infection suggest the existence of parasite strains that may vary in pathogenicity to the domestic cat and offer an explanation for the survival of some infected cats in more recent case studies.
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