Mast cells are white blood cells involved in the immune response, in particular, allergic reactions and inflammation. They are produced in the bone marrow before maturing and residing in connective tissue and the mucosal surfaces of the gut and lungs.
They contain histamine, heparin, cytokines and inflammatory mediators which are released when triggered by an antigen. This series of events results in an allergic reaction due to smooth muscle contraction, vasodilation and increased vascular permeability.
Diagnosis and grading:
MCTs are more commonly found in Shar-Pei’s, Boxers, Labradors, French Bulldogs and Golden Retrievers 1 and are more prevalent in middle-aged to older dogs. Whilst juvenile patients can suffer from MCTs, the prognosis is generally more favourable.
MCTs often appear as a lump in or under the skin and can frequently fluctuate in size as the result of manipulation or irritation. Ulceration can also occur. Systemic symptoms associated with the release of histamine and inflammatory mediators can be seen on occasion.
Diagnosis is made via sampling the mass, either by fine needle aspiration (FNA) or surgical biopsy/excision. Biopsy/excision is the preferred method as it provides a definitive diagnosis, grading and the ability to develop chemotherapy treatment plans. Further imaging such as ultrasonography or computed tomographic (CT) imaging can be performed to check for metastasis.
The behaviour of each individual mast cell tumour is assessed using many factors, the most reliable of which are obtained after the tumour is removed or an incisional biopsy performed (e.g. grade, mitotic index, and proliferation indices). Other more subjective prognostic factors exist, which are based on clinical examination findings and the tumour’s history, for example the tumour’s anatomic location, the presence of ulceration, the presence of systemic signs of disease, tumour size, rate of growth and recurrence after surgery. A combination of all these factors will indicate the prognosis and dictate the treatment plan.
Treatment:
Surgical: This is the mainstay of MCT treatment; MCTs are typically excised with wide lateral margins and a deep fascial plane to reduce the likelihood of regrowth. Depending upon the location of the MCT and subsequent skin defect, either primary closure can be performed or if required then skin reconstruction techniques such as local skin flaps or axial pattern flaps may be utilised.
Chemotherapy: This is used most commonly for high grade and/or metastatic MCTs or following incomplete excision.
Literature Update:
Our understanding of MCTs and their treatment is ever evolving, with several important and useful papers being published over the last few years. Some key points from these papers have been collated below:
- Mast cell tumours in dogs less than 12 months of age are associated with a more favourable prognosis than in more mature dogs. 2
- Planned narrow excision of appendicular mast cell tumours can provide tumour-free margins in as many as 74% of cases. 3
- Improved outcomes are observed when regional lymphadenectomy is performed in dogs with high-grade cutaneous mast cell tumours.4
- Lymph node metastasis is reported in 59% of cats with cutaneous low-grade mast cell tumours.5
- Sentinel lymph node mapping to ascertain the location of any possible nodal metastasis has been described, and differed from the regional lymph node in 57% of cases.6
References:
- Śmiech, A., Łopuszyński, W., Ślaska, B., Bulak, K. and Jasik, A. (2019). Occurrence and Distribution of Canine Cutaneous Mast Cell Tumour Characteristics Among Predisposed Breeds. Journal of Veterinary Research, [online] 63(1), pp.141–148. doi:https://doi.org/10.2478/jvetres-2019-0002.
- Rigas K, Biasoli D, Polton G, Finotello R, Murphy S, Di Palma S, Starkey M, Verganti S. Mast cell tumours in dogs less than 12 months of age: a multi-institutional retrospective study. J Small Anim Pract. 2020 Jul;61(7):449-457. doi: 10.1111/jsap.13181. PMID: 32715502.
- Haine DL, Pittaway R, Berlato D, Demetriou J. Incomplete histological margins following planned narrow excision of canine appendicular soft tissue sarcomas and mast cell tumors, using the residual tumor classification scheme. Vet Surg. 2022 Oct;51(7):1078-1086. doi: 10.1111/vsu.13852. Epub 2022 Jul 13. PMID: 35830150; PMCID: PMC9912198.
- Chalfon C, Sabattini S, Finotello R, Faroni E, Guerra D, Pisoni L, Ciammaichella L, Vasconi ME, Annoni M, Marconato L. Lymphadenectomy improves outcome in dogs with resected Kiupel high-grade cutaneous mast cell tumours and overtly metastatic regional lymph nodes. J Small Anim Pract. 2022 Sep;63(9):661-669. doi: 10.1111/jsap.13525. Epub 2022 Jun 22. PMID: 35733233.
- Arz R, Chiti LE, Krudewig C, Grieco V, Meier V, Fejös C, Stefanello D, Nolff MC. Lymph node metastasis in feline cutaneous low-grade mast cell tumours. J Feline Med Surg. 2023 Jan;25(1):1098612X221138468. doi: 10.1177/1098612X221138468. PMID: 36638145; PMCID: PMC10812050.
- Annoni M, Borgonovo S, Aralla M. Sentinel lymph node mapping in canine mast cell tumours using a preoperative radiographic indirect lymphography: Technique description and results in 138 cases. Vet Comp Oncol. 2023 Sep;21(3):469-481. doi: 10.1111/vco.12906. Epub 2023 May 16. PMID: 37191042.
