2. Mast Cell Tumours
• 16-21% of all cutaneous tumours
• Primarily a disease of older dogs
• No gender predilection
• Several breeds have an increased
incidence
3. Brodie
• 6 year old, male
neutered Labrador
• 8x5cm mass on the
right flank
• Clinical exam:
– BAR
– HR 80 bpm
– LNs not enlarged
– Abdominal palpation
was comfortable
7. Kiupel Grading System
• Differentiates MCTs into either high or low grade
based on:
– At least 7 mitotic figures in 10 hpfs
– At least 3 multinucleated cells in 10 hpfs
– At least 3 bizzare nuclei in 10 hpfs
– Karyomegaly
14. Treatment – Low Grade (I and
II)
• Surgery with wide margins
• Amputation
• Cytoreductive surgery and
radiotherapy
• Cytoreductive surgery and
chemotherapy
15.
16.
17. Treatment – High Grade (III)
• Wide surgery and chemotherapy +/-
radiotherapy
• Chemotherapy options are
– Vinblastine and Prednisolone
– Lomustine
– Tyrosine Kinase inhibitors (Masitinib or
Toceranib)
18. Management
• Re-evaluate regularly for local
reoccurrence or metastases
• Local site and regional lymph node
evaluation
• Complete physical exam
• Aspiration of any new cutaneous
masses or enlarged lymph nodes
20. References
• Dobson J, Duncan B and Lascelles X
(2003) BSAVA Manual of Canine and
Feline Oncology Second Edition. BSAVA
Withrow and MacEwan Small Animal
Clinical Oncology Fifth Edition.
Elsevier Saunders
• Bowlt K, Starkey M and Murphy S
(2014) Cutaneous Mast Cell Tumours
in Canines – diagnosis and staging.
Veterinary times 38, 29-30
Mast cell tumours are the most common cutaneous tumours in the dog, accounting for 16-21% of all cutaneous tumours. They are primarily a disease of older dogs but they have been reported in younger dogs. There is no gender predilection. Several breeds have an increased incidence of mast cell tumours. There breeds include Boxers, English Bulldogs, Labradors, Golden Retrievers, Cocker spaniels, Sharpeis. This is suggestive of an underlying genetic cause and studies are currently on-going to determine this.
Brodie is a 6 year old MN lab that presented to the oncology service for investigation and treatment of a 8x5cm mass that was removed from his right flank by the referring vet on the 12th of September. Initially the mass was thought to be a lipoma so the o agreed to monitor at home but excision was agreed when the mass increased in size.
MCT have a wide range of presentations and it is not uncommon for them to be misinterpreted as Lipomas. They tend to be raised, hairless, solitary, slow-growing tumours that have been present for several months. Undifferentiated MCT tend to be rapidly growing, ulcerated lesions that cause considerable irritation and attain a large size.
O may describe the mass as changing in size and becoming red. This is known as the Darier’s sign and it occurs as a result of vasoactive amine release. Heparin allows an increase in local bleeding, whilst histamine causes local oedema. The change in size occurs due to the spontaneous degranulation. Other clinical signs which may be reported are vomiting, anorexia, melaena and abdominal pain although dogs can present and vomiting and melanea as their primary concern. These occur due to excessive histamine levels secondary to MC degranulation and stimulation of H2 receptors in gastric parietal cells. Care must be taken when manipulating MCT as can cause degranulation.
Initial investigation generally consists of a FNA. A diagnosis can be obtained by cytology alone in 96% of cases and most MCT tumours are diagnosed using cytology. The RVS did not do cytology in Brodie’s case as the owners were happy to monitor the mass at home and then opted for surgery when the mass began to increase in size.
Histological grade is the single most important prognostic factor as it is considered the most consistent and reliable; although it will not predict the behaviour of every tumour. MCT that show malignant behaviour spread to the local lymph node, then classically to the liver and spleen. Histology can be performed on a biopsy of the mass or after the mass has been surgically excised.
There are currently 2 grading systems in use when evaluating MCT. The original grading system described by Patnaik and others is based on cell morphology and tumour invasiveness into normal surrounding tissues. Using this system the majority of well differentiated MCT will not metastasise and adequative treatment of the primary lesion will be curative while more than 75% of the poorly differentiated masses will metastasise.
The issue with this grading system is that it is subjective resulting in less than a 64% agreement between pathologists for grade 1 and 2 MCT and 75% aggreement for grade 3.
In order to reduce the subjectivity; a two tier system was described by Kiupel. This system attempts to differentiate MCTs into high or low grade using the above criteria. If the above criteria are met the tumour is described as high grade.
Histology revealed that Brodie had a Grade 11 MCT which extended to the margins. Mitoses were not seen in 10 random high power field and anisocytosis and anisokaryosis was minimal to moderate. These changes correspond to a low-grade MCT on the Kiupel scale.
MCT metastasise to the local lymph node, liver, spleen and bone marrow (rarely the lungs) and so it is important to assess these organs when staging the disease.
In Brodie’s case we used haematology, biochemistry, abdo us, splenic FNA and thoracic radiographs. Haematology and biochemistry were unremarkable other than a mildly low albumin at 27g/L (29-36).
No abnormalities were detected on ultrasound.
An FNA of the spleen was taken and submitted for cytology. The cytology report suggested that the number of mast cell was increased. This could be a resident mast cell population but metastatic disease could not be ruled out.
Thoracic radiographs revealed a bronchial lung pattern but this is likely to be incidental at this age and mild remodelling of the shoulder but no lesions indicative of metastases could be identified).
Low Grade (I and II):
Surgery – in well differentiated tumours this has the potential for cure. The recommendation is to take wide surgical margins (2-3cm) laterally and resect to a clean fascial plane deep to the tumour. It is important to send the excised tissue for histopathology to ensure that appropriate margins have been achieved. This was not achieved in Brodie’s case.
Amputation is an option if appropriate margins cannot be achieved.
Surgery with appropriate margins may not be an appropriate due to the location of the MCT e.g. extremities. Therefore cytroreduction therapy can be combined with radiotherapy (12 treatments in total). Cytoreduction will reduce the disease to stage 0 (incomplete microscopic margins). Two-year control rates of 85-95% can be expected for low or intermediate grade 0 tumours (incomplete margins). Some studies suggest prophylactic nodal irritation but due to the low risk of postsurgical metastases this is probably not required.
Cyrtoreduction and chemotherapy – this can be used if radiotherapy is not available or not affordable
If the planned curative excision is unsuccessful and appropriate margins were not achieved; as in Brodie’s case the options are:
Second excision of the surgical scar with wide margins
Radiotherapy
Brodies owners decided in this cases that a further ultrasound and FNA of the spleen in 3 months time was not necessary. They did not wish to progress with radiotherapy or chemotherapy so felt the sedation and examination would not be necessary.
