Nuclear morphometry in cytopathology: a prognostic indicator for canine cutaneous mast cell tumors

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.

Prognostic Value of Intratumoral Collagen Quantification in Canine Oral Melanomas

The majority of the melanocytic neoplasms are considered malignant and highly metastatic. However, a subset of the melanocytic tumors has a more favorable prognosis and the identification of precise prognostic markers for this neoplasm may be useful to guide treatment. The collagen architecture and density have been shown to correlate with tumor progression in human breast cancer and canine mast cell tumors. The purpose of the present study was to investigate the prognostic value of the intratumoral collagen index (ICI) as an indicator of postsurgical survival and its relation with other prognostic markers for canine oral melanomas (OMs). Twenty-two cases were tested for intratumoral collagen density using Masson's trichrome stain and morphometry. No differences were found between dogs regarding survival. The ICI was not correlated with proliferative activity or nuclear atypia. The results presented herein indicate that the quantity of intratumoral collagen in canine OMs is not an efficient indicator of postsurgical survival. Complementary studies about the expression and activity of enzymes that are capable of degrading extracellular matrix (ECM) components are necessary.

Canine mast cell tumors: utility of stereologic tools in cytology

Quantitative morphologic parameters assessed in cytologic samples of canine cutaneous mast cell tumors (ccMCTs) may assist with surgical planning and prognostication. Robust cutoffs can be defined, with high reproducibility, for parameters such as the nuclear area (NA). The NA may be determined by morphometry (image analysis, NAI) or by stereology, such as the 2D-nucleator method (NAN); stereologic techniques have not been applied to cytologic specimens of ccMCT, to our knowledge. We retrospectively selected routine cytology smears from 51 ccMCT cases and screened them to determine the percentage of neoplastic mast cells with indistinct nuclear borders; this was repeated after the slides were restained with H&E. The NAI and the NAN were estimated in 100 mast cells per animal in H&E-stained slides. All nuclei were visible in H&E smears, and unbiased quantification was feasible. The NAN was similar to NAI, but less time-consuming. Both the NAN and NAI determined by cytology differed in histologic low- and high-grade ccMCTs, and in histologic grade I plus II versus grade III ccMCTs. Stereologic parameters such as the NAN could be considered as complementary techniques for the cytologic evaluation of ccMCTs.

Stereology in Grading and Prognosis of Canine Cutaneous Mast Cell Tumors

Canine cutaneous mast cell tumors (ccMCTs) are currently graded according to Patnaik and Kiupel grading schemes. The qualitative and semiquantitative parameters applied in these schemes may lead to inter- and intraobserver variability. This study investigates the prognostic value of volume-weighted mean nuclear volume (vv¯), a stereological estimation that provides information about nuclear size and its variability. vv¯ of 55 ccMCTs was estimated using the “point-sampled intercept” method and compared with histological grade and clinical outcome. The clinical history of dogs treated with surgical excision alone was available for 30 ccMCTs. Statistical differences in vv¯ were found between grade II (x¯ = 115 ± 29 µm³) and grade III ccMCTs (x ¯= 197 ± 63 µm³), as well as between low-grade (x ¯= 113 ± 28 µm³) and high-grade ccMCTs (x¯ = 184 ± 63 µm³). An optimal cutoff value of vv¯ ≥ 150 µm³ and vv¯ ≥ 140 µm³ was determined for grade III and high-grade ccMCTs, respectively. In terms of prognosis, vv¯  was not able to predict the clinical outcome in 42% of the cases; however, cases with vv¯ <125 µm³ had a favorable outcome. These results indicate that, despite having limited prognostic value when used as a solitary parameter, vv¯ is highly reproducible and is associated with histological grade as well as with benign behavior.

Intratumoral collagen index predicts mortality and survival in canine cutaneous mast cell tumours

BACKGROUND

Mast cell tumours (MCTs) constitute almost 25% of cutaneous neoplasms in dogs. Their biological behaviour is predicted using histopathological grading which is based on several subjective criteria that are vulnerable to intra- and interobserver variability. To improve the prediction of the biological behaviour, several complementary markers have been studied. The integrity of the extracellular matrix (ECM) may play a protective role against tumoral progression, and favour cellular proliferation, angiogenesis, invasion and metastases when altered.

HYPOTHESIS/OBJECTIVES

To evaluate the quantification of collagen and elastic fibres as prognostic markers for MCTs.

ANIMALS

Thirty-eight random cases of canine cutaneous MCT surgically treated with wide margins were included.

METHODS AND MATERIALS

Intratumoral collagen and elastic fibres were identified and quantified on histological sections stained with Masson's trichrome, Picrosirius red and Verhoeff; the results were compared with histopathological grades, mortality due to the disease and postsurgical survival.

RESULTS

Morphometric analysis revealed a significant relationship between histopathological grade and intratumoral collagen index (CoI). In addition, the CoI was considered an independent indicator for mortality and postsurgical survival.

CONCLUSIONS AND CLINICAL IMPORTANCE

These results support the importance of the CoI in the grading and prognosis of MCTs, suggesting that preservation and/or synthesis of collagen have the potential to become targets for MCT therapeutics.

Quantitative Morphology as a Prognostic Factor in Feline Spontaneous Cutaneous Squamous Cell Carcinomas

In a study on cytological specimens from 30 cats with histologically confi rmed cutaneous squamous cell carcinoma, the morphometric variables mean nuclear area (MNA, μm2), mean nuclear perimeter (MNP, μm), mean nuclear diameter (D mean, μm), minimum nuclear diameter (D min, μm) and maximum nuclear diameter (D max, μm) were studied and compared to metastases in regional lymph nodes. The mean values of these parameters were signifi cantly greater in cats with lymph node metastases compared to parameters of tumour cells from cats which were lymph node-negative. A signifi cant positive correlation was observed between all studied morphometric parameters and metastases in the regional lymph nodes. In conclusion, computer -assisted nuclear morphometry could be used as a prognostic method in the diagnosis of spontaneous feline cutaneous squamous cell carcinomas.

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.

Increased expression of tissue inhibitor of metalloproteinase-1 correlates with improved outcome in canine cutaneous mast cell tumours

Canine mast cell tumour (MCT) is a biologically heterogeneous disease. The extracellular matrix degradation promoted by matrix metalloproteinases (MMPs) has been studied in an attempt to elucidate the mechanisms involved in the biological behaviour of tumours. The aim of this study was to characterize the expression of MMP-2 and -9 and tissue inhibitors of metalloproteinase (TIMP)-1 and -2 in canine cutaneous MCTs and to evaluate their prognostic values. Immunohistochemical staining for MMP-2, MMP-9, TIMP-2 and TIMP-1 was performed in 46 canine cases of MCTs. TIMP-1 expression showed an independent prognostic value for post-surgical survival and disease-related mortality. Dogs with MCTs showing less than 22.9% mast cell TIMP-1 positivity were more prone to die because of the disease and had a shorter post-surgical survival. This article suggests the involvement of TIMP-1 in MCT progression, by contributing to a good outcome in patients with MCTs.

Cytomorphometry of serosal effusion in dogs

Cytomorphometry made on cytological slides is the quantitative method of precise analysis of cellular structures, including both cytoplasm and nucleus. The aim of this study was to describe cytomorphometric parameters of mesothelial cells in the course of benign reactive and malignant proliferation and to compare them to carcinomas and adenocarcinomas located within serosal cavities in dogs. The second aim was to evaluate applicability of cytomorphometry to diagnostics of diseases causing accumulation of effusion in serosal cavities. Cytological samples of normal and non-malignant mesothelium, mesothelioma and various carcinomas were collected from dogs. Cytomorphometry was made on the smears stained with Giemsa solution. Mean nuclear and cellular perimeter, mean nuclear and cellular area, mean nuclear and cellular diameter, and mean nuclear and cellular roundness were determined. Moreover, nuclear to cytoplasmic ratio (N/C) was calculated. The data revealed statistically significant differences for all parameters, excluding mean nuclear perimeter, between compared groups. Normal mesothelium cells and their nuclei were significantly smaller and more elongated than cells and nuclei of both benign reactive and malignant neoplastic mesothelium. Only a few differences were observed between benign reactive mesothelium cells and mesothelioma cells - mean nuclear area and mean nuclear diameter of benign reactive mesothelium cells were significantly larger and N/C ratio was higher in comparison to mesothelioma cells. Even though some significant differences were observed, considerable overlap of these cytomorphometric parameters in animals with different diseases limited practical role of these observations. Cytomorphometric analysis of cellular samples collected from dogs with proliferative processes affecting serosal cavities can be only an auxiliary method increasing accuracy of preoperative diagnosis.

Comparative analysis of markers of cell proliferation in canine mast cell tumours according to current classifications

The study aimed at immunohistochemical analysis of various markers of cell proliferation and comparison of the results with canine mast cell tumours grading systems according to the Patnaik and Kiupel. Tissue sections were stained using classical technique with haematoxylin and eosin, and immunohistochemical studies were performed with Ki-67, PCNA and MCM-3 antibodies. Additionally the mitotic index was assessed. Statistical analysis including rank correlation Spearman's and ANOVA Friedman analysis was performed. The significance was set at p<0.05. Expression of all examined antigens was detected. The results obtained allow concluding that there is a strong relationship between all the cell markers. However, due to the very strong response and positive reaction in the majority of tumours PCNA is not recommended as a prognostic indicator. Ki-67 and MCM-3 can be successfully used in the evaluation of canine mast cell tumours.

In vivo model for mastocytosis: A comparative review

Human mastocytosis are heterogeneous group of neoplastic diseases characterized by a different degree of uncontrolled mast cell (MC) proliferation and activation. Interestingly, human mastocytosis share several biological and clinical features with canine mast cell disorders, so called canine mast cell tumors (CMCTs). These CMCTs are the most common spontaneous cutaneous tumors found in dogs representing a valid model to study neoplastic mast cell disorders. It has been discovered that the pathological activation of c-Kit receptor (c-KitR), expressed by MCs, has been involved in the pathogenesis of neoplastic MC disorders. In this review we have focused on human mastocytosis in terms of: (i) epidemiology and classification; (ii) pathogenesis at molecular levels; (iii) clinical presentation. In addition, we have summarized animal models useful to study neoplastic MC disorders including CMCTs and murine transgenic models. Finally, we have revised therapeutic approaches mostly common in human and canine MCTs and novel tyrosine kinase inhibitors approved for CMCTs and recently translated in human clinical trials.

Utility of nuclear morphometry in the cytologic evaluation of canine cutaneous soft tissue sarcomas

Cytopathologists lack reliable criteria to distinguish neoplastic from reactive spindle cells; however, with computer-based nuclear morphometry, it is now possible to more objectively and precisely quantify differences between selected populations of cells. Forty-four cutaneous soft tissue sarcomas and 5 cases of reactive spindle cell proliferations in the dog were morphometrically analyzed with regard to median and standard deviation (SD) of nuclear area, diameter (max, min, mean), radius (max, min), perimeter, and roundness. Overall, nuclei from reactive spindle cells were larger, with greater variation in nuclear size and shape. Significant differences ( P < 0.05) were found for several nuclear parameters, including the median and SD of maximum diameter and radius, as well as the SD of roundness. No significant differences were found in nuclear parameters between soft tissue sarcomas divided by histologic grade, mitotic index, or tumor necrosis score. Analysis of the sources of variation indicated near-perfect intraobserver and substantial interobserver agreement. The largest source of variation was due to selection of different measurement fields, reflecting the inherent biological variation in nuclear size within the tumor cell population. The results indicate that nuclear morphometry on cytologic preparations is a reproducible method that may be able to differentiate cutaneous soft tissue sarcomas from reactive mesenchymal lesions in the dog. Further studies, including a larger number of cases, are warranted to assess repeatability of results.

Proposal of a 2-tier histologic grading system for canine cutaneous mast cell tumors to more accurately predict biological behavior

Currently, prognostic and therapeutic determinations for canine cutaneous mast cell tumors (MCTs) are primarily based on histologic grade. However, the use of different grading systems by veterinary pathologists and institutional modifications make the prognostic value of histologic grading highly questionable. To evaluate the consistency of microscopic grading among veterinary pathologists and the prognostic significance of the Patnaik grading system, 95 cutaneous MCTs from 95 dogs were graded in a blinded study by 28 veterinary pathologists from 16 institutions. Concordance among veterinary pathologists was 75% for the diagnosis of grade 3 MCTs and less than 64% for the diagnosis of grade 1 and 2 MCTs. To improve concordance among pathologists and to provide better prognostic significance, a 2-tier histologic grading system was devised. The diagnosis of high-grade MCTs is based on the presence of any one of the following criteria: at least 7 mitotic figures in 10 high-power fields (hpf); at least 3 multinucleated (3 or more nuclei) cells in 10 hpf; at least 3 bizarre nuclei in 10 hpf; karyomegaly (ie, nuclear diameters of at least 10% of neoplastic cells vary by at least two-fold). Fields with the highest mitotic activity or with the highest degree of anisokaryosis were selected to assess the different parameters. According to the novel grading system, high-grade MCTs were significantly associated with shorter time to metastasis or new tumor development, and with shorter survival time. The median survival time was less than 4 months for high-grade MCTs but more than 2 years for low-grade MCTs.