Patient and tumour factors influencing canine mast cell tumour histological grade and mitotic index

Primary preputial reconstruction following surgical excision of cutaneous mast cell tumours without penile amputation in eight dogs

CASE HISTORY

Medical records from a single referral hospital (Davies Veterinary Specialists, Hitchin, UK) were reviewed to identify dogs (n = 8) with preputial cutaneous mast cell tumours (CMCT) that underwent surgical excision and primary preputial reconstruction, preserving the penis and urethra, after clients declined alternatives such as penile amputation and urethrostomy, from June 2017-June 2022.

CLINICAL FINDINGS

Tumours had a median diameter of 21.5 (min 15, max 30) mm, were located cranioventrally (3/8), caudoventrally (1/8), laterally (2/8) and dorsally (2/8) relative to the prepuce and were diagnosed as CMCT based on cytology. No dogs had hepatic or splenic metastasis on cytology but inguinal lymph node metastasis was identified in 3/4 dogs sampled.

TREATMENT AND OUTCOME

The owners of all dogs had declined penile amputation and scrotal urethrostomy. The CMCT were excised and primary reconstruction of the prepuce performed. Surgical lateral margins of 10, 20 or 30 mm were used and the deep margin excised the inner preputial lamina or underlying muscular fascia. The deep margin for caudoventral CMCT involved excision of the underlying SC adipose tissue. Preputial advancement was performed in 3/8 dogs to achieve adequate penile coverage. Histopathology confirmed all CMCT were Kiupel low grade, Patnaik grade II with complete margins in 6/8 dogs but identified metastasis only in one inguinal lymph node from one dog. Two dogs encountered minor complications (infection and a minor dehiscence) and one dog had a major complication (infection with major dehiscence). Median follow-up duration was 125 weeks, excluding one dog with 4 weeks of follow-up. None of the dogs experienced local recurrence or died of mast cell disease during the available follow-up period.

CLINICAL RELEVANCE

 This clinical study evaluated a surgical alternative to penile amputation and advanced reconstructive techniques for Kuipel low/Patnaik grade II preputial CMCT when these procedures were declined by owners. Surgical excision of preputial CMCT with lateral margins of 10, 20 or 30 mm with primary preputial reconstruction is achievable with low morbidity and a good outcome when penile amputation and scrotal urethrostomy is not an option.

Eyelid and conjunctival mast cell tumors: A retrospective study of 26 dogs and 8 cats

OBJECTIVE

The objective of the study was to describe clinical and histologic characteristics of eyelid (LMCT) and conjunctival (CMCT) mast cell tumors in dogs and cats presented to a referral clinic in Germany.

ANIMAL STUDIED

Medical records were reviewed to identify dogs and cats diagnosed with LMCTs or CMCTs between 2006 and 2020.

RESULTS

LMCT were diagnosed in 31 patients and were cutaneous (n = 28; 20 dogs and 8 cats) or subcutaneous (three dogs). Five cases involved the mucocutaneous junction (four dogs, one cat). CMCTs occurred only in dogs (n = 3). At the time of presentation two of the four canine LMCT cases involving the mucocutaneous junction had metastasized to a mandibular lymph node. When applying the Kiupel system, both these cases were categorized as high grade. 85.7% (18/21) of the canine (19 cutaneous and 2 subcutaneous) LMCT and all CMCT cases were categorized as Kiupel low grade. No local recurrences occurred in all LMCT cases in which clean surgical margins were obtained (n = 18, mean surgical margin width: dogs 9.4 mm, cats 3.8 mm). Two cats (2/4) and four dogs (4/7) with questionable or incomplete surgical margins experienced local recurrences (mean time to recurrence of 180 and 637 days in dogs and cats, respectively).

CONCLUSION

Recurrence of low-grade LMCTs and CMCTs following excision with clean margins is rare. Tumors involving the mucocutaneous junction may be of higher grade and prone to lymphatic metastasis.

Epidemiology of canine cutaneous round cell tumours on the canary archipelago in Spain

In this study we undertook a comprehensive analysis of a Pet Tumour Registry of the Canary Archipelago (PTR-CA) in Spain to investigate the epidemiology of canine cutaneous round cell tumours. From a database of 2526 tumours collected from 2003 to 2020, we conducted a longitudinal analysis of the main trends in diagnosis, age, multiplicity and anatomical distribution as well as a case-control study comparing these cases with the contemporaneous canine population of the Canary Archipelago to analyse breed distribution. In line with former studies, we found histiocytomas mostly affect young dogs (2, IQR 1-5) and mast cell tumours affect middle-to-old dogs (8, IQR 6-10) with grade 1 affecting at younger ages (6.5, IQR 6-8) than both grade 2 (8, IQR 6-10 years) and grade 3 (9, IQR 7-11). Histiocytomas and plasmacytomas showed a similar anatomical distribution appearing mainly on the face, head and neck regions while mast cell tumours occur mainly on limbs and trunk. Higher risk for mast cell tumours and histiocytomas were found for Bulldog-related breeds such as Boxer (ORMCT  = 23.61, CI95%: 19.12-29.15, ORHCT  = 10.17, CI95%: 6.60-15.67), Boston Terrier (ORMCT 19.47, CI95%: 7.73-49.05, ORHCT 32.61, CI95%: 11.81-90.07) and Pug (ORMCT 8.10, CI95%: 5.92-11.07, ORHCT 7.87, CI95%: 4.66-13.28) while Chihuahua dogs showed significantly less risk (ORMCT 0.18, CI95%: 0.09-0.33, ORHCT 0.41, CI95%: 0.21-0.78). Notably, the Canarian Mastiff, a local breed, had a low risk of suffering from a mast cell tumour which raises the question of whether this relates to a genetic peculiarity of this breed or some husbandry and environmental factor.

Immunohistochemical and Molecular Genetic Analysis of Canine Digital Mast Cell Tumours

Grading, immunohistochemistry and c-kit mutation status are criteria for assessing the prognosis and therapeutic options of canine cutaneous mast cell tumours (MCTs). As a subset, canine digital MCTs have rarely been explored in this context. Therefore, in this retrospective study, 68 paraffin-embedded canine digital MCTs were analysed, and histological grading was assessed according to Patnaik and Kiupel. The immunohistochemical markers KIT and Ki67 were used, as well as polymerase chain reaction (PCR) for mutational screening in c-kit exons 8, 9, 11 and 14. Patnaik grading resulted in 22.1% grade I, 67.6% grade II and 10.3% grade III tumours. Some 86.8% of the digital MCTs were Kiupel low-grade. Aberrant KIT staining patterns II and III were found in 58.8%, and a count of more than 23 Ki67-positive cells in 52.3% of the cases. Both parameters were significantly associated with an internal tandem duplication (ITD) in c-kit exon 11 (12.7%). French Bulldogs, which tend to form well-differentiated cutaneous MCTs, had a higher proportion of digital high-grade MCTs and ITD in c-kit exon 11 compared with mongrels. Due to its retrospective nature, this study did not allow for an analysis of survival data. Nevertheless, it may contribute to the targeted characterisation of digital MCTs.

Tumour Incidence in Dogs in Germany: a Retrospective Analysis of 109,616 Histopathological Diagnoses (2014-2019)

Characterization of a tumour entity is based on the precise histopathological diagnosis taking into account the signalment of the diseased animal. The present study is a comprehensive, up-to-date statistical investigation on the type, frequency and breed distribution of neoplasia in dogs in Germany. The histopathological datasets of 109,616 German canine tissue samples (2014-2019) were processed and statistically examined in retrospect. Non-neoplastic diseases were found in 38,650 samples (35.3%) and 70,966 neoplasms (64.7%) were diagnosed. The most common neoplasms were mammary tumours (21.9%), benign epithelial skin tumours (15.4%), mast cell tumour (9.7%), histiocytoma (7.0%), soft tissue sarcoma (5.8%), lipoma (5.8%), melanocytic tumours (5.2%) and odontogenic tumours (4.7%). In general, Beagles, Magyar Vizslas, Boxers, Schnauzers, Spaniels, French Bulldogs and Golden Retrievers had an increased risk of neoplasia (odds ratio 1.17-1.46; all: P ≤0.001) compared with crossbreed dogs. In particular, Boxers, Golden Retrievers, Rottweilers and Schnauzers were often affected by malignant neoplasms, whereas some breeds (eg, West Highland White Terrier, Magyar Vizsla, Chihuahua, Dachshund and Yorkshire Terrier) were frequently affected by numerous benign tumour types. Despite the known risk of haemangiosarcoma in German Shepherd Dogs, other malignant tumours were rare in this breed. Depending on the type of tumour, some purebred dog breeds can have an increased, reduced or identical risk for certain neoplasms compared with crossbreeds. Discussion of breed predispositions to tumour diseases must therefore be conducted critically and with a view to clinical relevance.

Evaluation of Tumor Grade and Proliferation Indices before and after Short-Course Anti-Inflammatory Prednisone Therapy in Canine Cutaneous Mast Cell Tumors: A Pilot Study

Glucocorticoid administration is a common clinical practice that attempts to decrease the inflammation associated with and improve the resectability of canine mast cell tumors (MCTs). However, the impact of neoadjuvant glucocorticoids on the histological features and proliferation indices of canine MCTs is unknown. The objective of this study was to evaluate changes in tumor grade, mitotic count, Ki67, AgNOR, and AgNORxKi67 scores following short-course anti-inflammatory neoadjuvant prednisone in canine patients with MCTs. This was a prospective single-arm pilot study. Client-owned dogs with treatment-naïve cytologically confirmed MCTs were enrolled. Patients underwent an initial incisional biopsy followed by a 10–14-day course of anti-inflammatory prednisone and surgical resection. All histological samples were randomized, masked, and evaluated by a single pathologist. Unstained paired pre- and post-treatment samples were submitted to a commercial laboratory for Ki67 and AgNOR immunohistochemical analysis. There were 11 dogs enrolled with 11 tumors. There were no statistical differences between the pre- and post-treatment histological parameters of mitotic index, Ki67, AgNOR, or Ki67xAgNOR. There were no clinically significant alterations between pre-treatment and post-treatment in the assignment of tumor grades. A short course of anti-inflammatory prednisone does not appear to alter the histological parameters that affect grade determination or significantly alter the proliferation indices in canine MCTs.

Canine mast cell tumours part I: Clinical and survival outcomes

BACKGROUND

Dogs have a species-specific susceptibility for developing mast cell tumours (MCTs). Mutations in the KIT proto-oncogene (KIT) are known to contribute to the neoplastic biology of mast cells. In dogs, the most common KIT mutation is an internal tandem duplication (ITD) in exon 11 which has been considered a useful prognostic supplement to traditional histopathological tumour grading.

OBJECTIVE

The aim of this retrospective study was to explore the importance of KIT exon 11 ITD mutation status and known clinical and pathological indices in predicting prognosis in a cohort of Australian dogs diagnosed with MCT.

METHODS

Clinical parameters, survival data, and KIT mutation status were collected and assessed for 220 dogs with cutaneous or subcutaneous MCT (n = 189 and n = 31, respectively).

RESULTS

In at least one of the multivariable models, tumour grade (cutaneous Kiupel low or high grade) or tumour subcutaneous location, multiple concurrent MCTs, metastasis at the time of surgery, and senior age were statistically significant in predicting the outcome (MCT-related death and/or second MCT diagnosis) at 6- or 12-month post-tumour excision. KIT exon 11 ITD mutation status was not a significant predictor in any of the final multivariable models and was strongly correlated with high histological grade (p < 0.001).

CONCLUSION

In this sample of dogs, tumour histological grading remained the single most powerful prognostic indicator for MCT outcome. However, concurrent evaluation of multiple prognostically significant parameters provides information of potential value to inform therapeutic management for each patient.

Intratumoural Treatment of 18 Cytologically Diagnosed Canine High-Grade Mast Cell Tumours With Tigilanol Tiglate

Canine high-grade mast cell tumours (HGMCT) are associated with a poor prognosis, are inherently more invasive, and have higher rates of local recurrence. The primary aim of this retrospective study was to assess the efficacy of intratumoural tigilanol tiglate (TT) as a local treatment option. Eighteen dogs with mast cell tumours (MCT) cytologically diagnosed by veterinary pathologists as either high-grade or suspected high-grade MCT were treated with TT. The TT dose was based on tumour volume (0.5 mg TT/cm³ tumour volume) and delivered intratumourally using a Luer lock syringe and a fanning technique to maximise distribution throughout the tumour mass. Efficacy was assessed on the presence/absence of a complete response (CR) to therapy at days 28 and 84 using response evaluation criteria in solid tumours (RECIST). For dogs not achieving a CR after 28 days, the protocol was repeated with a second intratumoural TT injection. Ten out of 18 dogs (56%) in this study achieved and maintained a CR to at least 84 days after their first or second treatment. Six patients were alive and available for evaluation at 2 years, three of those were recurrence free, and a further three patients were recurrence free following a second treatment cycle. Tigilanol tiglate shows efficacy for local treatment of HGMCT, with higher efficacy noted with a second injection if a CR was not achieved following the first treatment. In the event of treatment site recurrence (TSR), the tumour may be controlled with additional treatment cycles. Tigilanol tiglate provides an alternative local treatment approach to dogs with HGMCT that would either pose an unacceptable anaesthetic risk or the tumour location provides a challenge when attempting surgical excision.

Review of Histological Grading Systems in Veterinary Medicine

Tumor grading is a method to quantify the putative clinical aggressiveness of a neoplasm based on specific histological features. A good grading system should be simple, easy to use, reproducible, and accurately segregate tumors into those with low versus high risk. The aim of this review is to summarize the histological and, when available, cytological grading systems applied in veterinary pathology, providing information regarding their prognostic impact, reproducibility, usefulness, and shortcomings. Most of the grading schemes used in veterinary medicine are developed for common tumor entities. Grading systems exist for soft tissue sarcoma, osteosarcoma, multilobular tumor of bone, mast cell tumor, lymphoma, mammary carcinoma, pulmonary carcinoma, urothelial carcinoma, renal cell carcinoma, prostatic carcinoma, and central nervous system tumors. The prognostic relevance of many grading schemes has been demonstrated, but for some tumor types the usefulness of grading remains controversial. Furthermore, validation studies are available only for a minority of the grading systems. Contrasting data on the prognostic power of some grading systems, lack of detailed instructions in the materials and methods in some studies, and lack of data on reproducibility and validation studies are discussed for the relevant grading systems. Awareness of the limitations of grading is necessary for pathologists and oncologists to use these systems appropriately and to drive initiatives for their improvement.

Immunohistochemical Expression of Vascular Endothelial Growth Factor as a Prognostic Marker for Canine Mast Cell Tumors

Strong to moderate vascular endothelial growth factor (VEGF) expression may be a negative prognostic factor in canine mast cell tumors (MCTs). This study set out to determine the prognostic value of combined analysis of VEGF-A immunoreactivity, clinical presentation, patient staging, and tumor histologic grade in canine MCTs. In this study, intense VEGF staining was significantly associated with decreased survival (P = .025). Immunohistochemical expression of VEGF is not routinely employed as a prognostic factor in canine MCT workup. However, results of this study support the inclusion of this marker in the MCT prognostic panel. Investigation of VEGF expression may assist in the development of anti-VEGF drugs.