Mast cell tumours (mastocytosis) in the horse: A review of the literature and report of 11 cases

Mast cell tumours are uncommon tumours in horses, compared to some other species of domesticated animals. They are most frequently located in the skin, but they can also arise at other sites, including the upper respiratory tract and eye. Cytology or histopathology is required for diagnosis. Treatment options include surgical excision, laser ablation, cryotherapy, intralesional injection of corticosteroids or water, and radiotherapy. Malignant and systemic forms are very rare.     

Ultrasonographic findings in abdominal mast cell disease: a retrospective study of 19 patients

A retrospective survey from January 1989 to January 1999 of Tufts University Foster Hospital for Small Animals radiology records of 12 dogs and seven cats with cytologically or histopathologically confirmed abdominal mast cell disease was performed. Ultrasound changes in hepatic mast cell infiltration in dogs included a subjective increase in size, a diffuse increase in echogenicity, and one or more hypoechoic nodules. Ultrasound findings in the affected canine spleen included one or more hypoechoic nodules and a subjective increase in size. Two ultrasonographically unremarkable canine livers and one unremarkable spleen were found to be infiltrated by mast cells. The mast cell-infiltrated feline spleen was subjectively increased in size, mottled, irregular, or contained nodules. The affected lymph nodes in both dogs and cats were hypoechoic or inhomogeneous, subjectively increased in size, and rounded. Gastrointestinal involvement in cats was characterized by a thickened ileocecocolic junction or colon with loss of wall layering. Mast cells were not found in the gastrointestinal tract in any dog. One dog with mast cell infiltrate of the kidneys had multiple hypoechoic nodules in the cortex that distorted the outer contour of the kidney. Although these findings are not specific to the disease in either species, abdominal ultrasound is considered a useful tool for determining the extent of disease in small-animal patients with mast cell tumor if used in conjunction with histopathology or cytology.     

Histological and immunohistochemical features of cutaneous mast cell tumor in six captive four-toed hedgehogs (Atelerix albiventris)

This report described the histopathological and immunohistochemical features of cutaneous mast cell tumor (MCT) in six hedgehogs. The hedgehogs presented single cutaneous mass with ulcer and crusting. Histologically, the neoplastic lesions were characterized by the proliferation of well-differentiated mast cells (3 cases), and atypical mast cells (3 cases) with one atypical histiocytic morphology. Immunohistochemically, tumor cells were positive for KIT and mast cell tryptase, and were negative for Iba-1. In well-differentiated MCT, all patients were clinically improved and survived more than 365 days after surgical excision, whereas an atypical histiocytic MCT showed aggressive behavior with re-recurrence, and the animal died 115 days after surgery. These findings suggest that, compatible with other animals, well-differentiated MCT has a better prognosis in hedgehogs.     

Retrospective outcome evaluation for dogs with surgically excised,solitary Kiupel high‐grade,cutaneous mast cell tumours

Published outcomes for dogs with specifically high‐grade mast cell tumours (MCTs), controlled for clinical stage, are few. Clinical outcomes for 49 dogs with Kiupel high‐grade, clinical stage I, cutaneous MCTs were evaluated. Median survival time (MST) was 1046 days; 1 and 2‐year survival rates were 79.3% and 72.9%, respectively. At study end 24 dogs had died, 23 dogs were alive (median follow‐up 980 days) and 2 dogs were lost to follow‐up. Death was considered MCT‐related in 14 of 20 dogs with a known cause of death. Local tumour recurrence developed in nine dogs (18.4%); regional lymph node metastasis occurred in six dogs (12.2%); and a new MCT developed in 15 dogs (30.1%). Tumour location, histologic margin size and use of chemotherapy did not affect MST; increasing mitotic count (P = .001) and increasing tumour diameter (P = .024) were independently negatively prognostic. Six dogs that developed lymph node metastasis after surgery had worse MST (451 days) than 42 dogs that did not develop metastasis (1645 days); (P < .001). Our study suggests that dogs with local surgical control of clinical stage I histologically high Kiupel grade cutaneous MCT may have a long survival time; especially those with smaller tumours and a lower mitotic count. Our results suggest that evaluation of staging information and mitotic count may be equally helpful as histologic grading when making a prognosis; and highlight the importance of not relying on histologic grade alone when predicting survival for dogs with MCT.     

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 (OR_MCT = 23.61, CI95%: 19.12–29.15, OR_HCT = 10.17, CI95%: 6.60–15.67), Boston Terrier (OR_MCT 19.47, CI95%: 7.73–49.05, OR_HCT 32.61, CI95%: 11.81–90.07) and Pug (OR_MCT 8.10, CI95%: 5.92–11.07, OR_HCT 7.87, CI95%: 4.66–13.28) while Chihuahua dogs showed significantly less risk (OR_MCT 0.18, CI95%: 0.09–0.33, OR_HCT 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.     

Reconstruction of the lower eyelid by third eyelid lateral advancement and local transposition cutaneous flap after "en bloc" resection of squamous cell carcinoma in 5 cats

OBJECTIVE: To describe a novel technique for blepharoplasty to cover a tissue defect involving >/=50% of the lower eyelid. STUDY DESIGN: Prospective clinical study. ANIMALS: Five cats with lower eyelid squamous cell carcinoma (SCC). METHODS: En bloc resection of SCC by removing >/=50% of the lower lid with either the medial or lateral canthus was performed without other adjunctive treatment for SCC. The lid defect was reconstructed with a transposition skin flap derived from the frontal (medial defect) or temporal (lateral defect) region. The third eyelid was advanced laterally without dissection from its insertion; its outer conjunctival layer was removed, and the skin flap was sutured with single interrupted sutures dorsally over the nictitating membrane, ventrally to the cutaneous edge of the surgical wound and medially or laterally (depending on the canthus removed) to the skin of the remaining lower lid. RESULTS: Satisfactory cosmetic and functional results were achieved and the Schirmer tear tests were normal. In 2 cats, the skin flap needed monthly hair trimming to avoid corneal lesions. CONCLUSIONS: After en bloc resection of SCC involving >/=50% of the lower eyelid, reconstruction can be achieved by relocation of the third eyelid and use of a cutaneous transposition flap sutured to the scarified external surface of the third eyelid. Eyelid apposition and lacrimal function were preserved. CLINICAL RELEVANCE: Blepharoplasty using a cutaneous transposition flap sutured to the scarified surface of a relocated third eyelid should be considered for reconstruction of lower eyelid defects with >/=50% tissue loss of the lid margin.     

Magnetic resonance imaging of canine mast cell tumors

Mast cell tumors (MCT) are the most common cutaneous tumors in dogs. Our purpose was to describe the magnetic resonance (MR) imaging characteristics of cutaneous MCT and to identify imaging characteristics that allow differentiation of metastatic from normal lymph nodes. Eight dogs with a total of nineMCT were imaged as were their presumed draining and associated contralateral lymph nodes. The signal intensity of tumors and lymph nodes was compared to adjacent musculature. On T2-W images, 7/9 MCT were hyperintense to muscle and 2/9 were isointense. On T1-W images, 8/9 MCT were isointense and 1/9 were mildly hypointense. All tumors were strongly contrast enhancing; 5/9 were homogeneous and 4/9 heterogeneous in their enhancement patterns. Six lymph node pairs were included in the evaluation (five sentinel lymph nodes with metastases, one without, and six contralateral lymph nodes). Metastatic lymph nodes were significantly larger than their contralateral lymph nodes (P = 0.039). All lymph nodes were isointense on T1-W images and hyperintense on T2-W images. 5/5 metastatic and 2/7 normal lymph nodes were heterogeneously T2-hyperintense. All lymph nodes were moderately to strongly contrast enhancing. 4/5 metastatic and 2/7 normal lymph nodes had heterogeneous enhancement patterns. While heterogeneity was more common in metastatic than in normal lymph nodes, this difference was not significant (P = 0.058 for T2-W images; P = 0.234 for postcontrast images). MR imaging may be useful in the presurgical evaluation and clinical staging of cutaneous MCT.     

Pot-bellied Vietnamese pig with visceral mast cell tumors and mastocytemia

An approximately 12-year-old female Vietnamese Pot-Bellied Pig was presented to the Mississippi State College of Veterinary Medicine Food Animal Service for anorexia of 2 days duration. On physical examination, the patient appeared depressed and lethargic with significantly pale mucus membranes, open mouth breathing, and nostril flaring. On abdominal palpation, the abdomen was tense and uncomfortable. A complete blood count (CBC) and chemistry profile were performed. The CBC revealed significant anemia and mild leukocytosis characterized by mild neutrophilia with a left shift. Mast cells were rarely observed. Hematocrit = 8.1% (RI 22-50), RBC = 1.25 × 10⁶/μL (RI 3.6-7.8), WBC = 19.85 × 10³/μL (RI 5.2-17.9), Neutrophils = 15.08 × 10³/μL (RI 0-11.4), and Bands = 0.993 × 10³/μL (RI 0-0.019). The chemistry profile was unremarkable with a mildly elevated BUN and slightly decreased total protein and albumin (BUN = 39 mg/dL [RI 4.2-15.1], total protein = 6.2 g/dL [RI 6.6-8.9], and albumin = 2.5 g/dL [RI 3.6-5.0]). An abdominal ultrasound revealed numerous hypoechoic nodules diffusely scattered throughout the hepatic parenchyma. An FNA of one of the hepatic nodules was performed. A mild suppurative component and numerous variably granulated mast cells were observed. A presumptive cytologic diagnosis of mast cell tumor was made. Histopathology was performed, confirming the cytologic interpretation.     

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.     

Vinblastine and prednisolone chemotherapy for surgically excised grade III canine cutaneous mast cell tumours

The effect of treatment with vinblastine and prednisolone chemotherapy in dogs undergoing only surgical excision of Patnaik grade III cutaneous mast cell tumours is reported. Potential explanatory variables were explored using Kaplan–Meier survival analysis with log‐rank tests. During a median follow‐up period of 429 days, the overall median survival time (MST) was not reached (lower 95% CI = 322 days). The 1‐year survival probability was 0.71 (standard error 0.1), remaining unchanged at 2 years. Secondary disease at presentation was an independent risk factor for survival (P= 0.045). The MST of dogs presenting with secondary disease was 322 days, with a lower 95% confidence interval of 142 days and a 1‐year survival of probability of 0.47 (standard error 0.19). Adverse effects were recorded in 6 of the 108 (5.6%) vinblastine doses given. This chemotherapy regimen is a well‐tolerated adjunct to surgery for grade III mast cell tumours and appears to prolong survival compared with that expected with surgery alone.     

Multicentric mast cell tumors in a horse

Abstract: A 6‐year‐old female Rocky Mountain horse was presented for evaluation of draining tracts and distal limb subcutaneous edema on the left front and left hind limbs that had been present for 2 weeks. Direct smears of fluid collected by fine‐needle aspiration of subcutaneous fluid from both limbs were highly cellular with a predominance of eosinophils accompanied by numerous, moderately atypical, variably granulated mast cells. The cytologic diagnosis was mast cell tumor (MCT) with prominent eosinophilic infiltration with a differential diagnosis of eosinophilic granuloma. Histologic evaluation of surgical biopsies of lesions from both limbs was performed on sections stained with H&E, toluidine blue, and Luna stains. The histologic diagnosis was MCT, and staining with toluidine blue and Luna stains confirmed the presence of mast cells and eosinophils, respectively. In addition, the mast cells strongly expressed CD117. This is the first reported case of cutaneous mast cell neoplasia in a horse in which primary presenting complaints were draining tracts and distal limb subcutaneous edema involving multiple limbs. This case illustrates the utility of staining for CD117 expression in combination with traditional stains, such as toluidine blue and Luna, in differentiating MCTs from other eosinophilic lesions in horses.     

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.     

Evaluation of surgical margins required for complete excision of cutaneous mast cell tumors in dogs

OBJECTIVE: To determine whether neoplastic mast cells extended into tissue 1, 2, or 3 cm laterally or deeper than 1 fascial plane from the visible edge of cutaneous mast cell tumors (MCTs) in dogs. DESIGN: Prospective study. ANIMALS: 21 client-owned dogs with > or = 1 cutaneous MCT PROCEDURES: After preparation for surgery, each dog's skin was marked 1, 2, and 3 cm from the tumor edge at 0 degrees, 90 degrees, 180 degrees, and 270 degrees. At each 3-cm mark, deep fascia was exposed and sutured to the skin; the tumor was excised in routine fashion and fixed in formalin. Tumors were graded; margins were examined histologically for neoplastic mast cells. RESULTS: 23 cutaneous MCTs in 21 dogs were included in this study. Fifteen (65%) tumors were located on the trunk, 5 (22%) on the hind limbs, and 3 (13%) on the head and neck. There were 3 (13%) grade-I and 20 (87%) grade-II tumors. All grade-I tumors were completely excised at all margins. Seventy-five percent of the grade-II tumors were completely excised at the 1-cm margin, and 100% were completely excised at the 2-cm margin. Two grade-II MCTs located on the hind limbs of dogs were excised with a complete but close (within 1 mm) deep margin. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that a 2-cm lateral margin and a deep margin of 1 fascial plane appear to be adequate for complete excision of grade-I and -II MCTs in dogs.     

Surgical cytoreduction for the treatment of non-lymphoid vertebral and spinal cord neoplasms in cats: retrospective evaluation of 26 cases (1990–2005)

Medical records of 26 cats with non‐lymphoid vertebral and spinal cord neoplasms treated surgically were reviewed to determine outcome and prognostic factors for survival. Of the factors examined, only tumour phenotype was significantly associated with survival. Osteosarcoma (3/26 cats) and meningioma (16/26 cats) were the most common malignant and benign tumours, respectively. The median survival time for cats with malignant neoplasms was 110.5 days, compared with 518 days for cats with benign tumours. Cytoreductive surgery resulted in clinical improvement in 25/26 cats, but local treatment failure occurred in 10/26 cats. Overall, 19/26 cats died of confirmed (12/19) or suspected (7/19) tumour‐related causes, including all eight cats with malignant neoplasms. Results suggest that contemporary neurosurgical techniques commonly result in incomplete excision of feline non‐lymphoid vertebral and spinal cord tumours but are efficacious at palliation of clinical signs of spinal cord dysfunction.     

Eosinophilic conjunctivitis, herpes virus and mast cell tumor of the third eyelid in a cat

A 3-year-old Himalayan cat was diagnosed with concurrent eosinophilic conjunctivitis, herpes virus, and a conjunctival mast cell tumor. Eosinophilic conjunctivitis was verified via cytology from a conjunctival scraping, which revealed 50% eosinophils and 50% neutrophils. Herpes virus was verified via a positive polymerase chain reaction (PCR). Conjunctival scrapings for chlamydia immmunofluorescent antibody (IFA) and herpes IFA were negative. A mycoplasma was detected by a general mycoplasma PCR but the organism did not grow on the available mycoplasma media. The mass was excised and microscopic evaluation revealed a histiocytic mast cell tumor. The mast cell did not recur following local excision (at 1 year follow-up). The eosinophilic conjunctivitis was treated with both topical steroids and systemic megesterol acetate (Ovaban). When topical steroids were used, the herpes virus flared up and resulted in dendritic and geographic corneal ulceration. Therefore, the cat was treated with megesterol acetate and the eosinophilic conjunctivitis was well controlled. Treatment of eosinophilic conjunctivitis in the cat with megesterol acetate may be the treatement of choice due to the possibility of herpes virus.