Canis ISSN: 2398-2942

Skin: mastocytoma

Synonym(s): Mast cell tumor, Mastocytosis

Contributor(s): Laura Garrett, David Scarff


  • Most common malignant skin tumor of dog (20% of all canine cutaneous tumors) and most frequent scrotal tumor.
  • Signs: mass in predilection sites: trunk and perineal region (50%), skin of extremities (40%). Multiple masses may be seen.
  • Benign to highly malignant.
  • Diagnosis: cytology or histopathology.
  • Treatment: aggressive surgical resection/preputial amputation/ablation with or without radiotherapy/chemotherapy.
  • Prognosis: good for low-grade tumors; guarded to poor for high-grade.
    Print off the owner factsheet on Canine cutaneous mast cell tumours to give to your client.


Predisposing factors


  • Breed.


  • Although often feel like discrete masses, they invade microscopically beyond palpable margins.
  • Systemic signs (GI ulcerations) may be seen due to histamine release.
  • Can be classified (graded) as:
  • Well-differentiated Cytology well differentiated mast cell tumor :
    • Abundant purple cytoplasm.
    • Central dark nucleus.
    • Clear cell membrane.
    • Rare mitotic figures.
  • Intermediate:
    • Indistinct boundaries.
    • Pleomorphic cells.
    • Cells fused in syncytia.
    • Rare mitotic figures.
  • Poorly-differentiated Cytology intermediate - poorly differentiated mast cell tumor :
    • Heavy infiltration.
    • Sparse cytoplasm.
    • Irregular nucleus.
    • Frequent mitotic figures.
  • Vary from benign to highly malignant.
  • Mast cells may degranulate → histamine, heparin and other vasoactive amine release → local acute inflammation or systemic signs.
  • Sytemic effects:
    • Prolonged bleeding time Hematology: activated clotting time → heparin, action on clotting cascade.
    • Delayed wound healing → proteolytic enzymes released from tumor at surgery and release of fibroblast suppressor factor due to histamine binding to macrophage H1 and H2 receptors.
    • Anaphylaxis → sudden release of large amounts of histamine.
    • Gastrointestinal ulceration → histamine action on H2 receptors in stomach → increased gastric acid secretion and gastric hypermotility.


  • Weeks to years (depending on grade).


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Biasoli D, Compston-Garnett L, Ricketts S L et al (2019) A synonymous germline variant in a gene encoding a cell adhesion molecule is associated with cutaneous mast cell tumour development in Labrador and Golden Retrievers. PLoS Genet 15(3), e1007967 PubMed.
  • London C A et al (2009) Multi-center, placebo-controlled, double-blind, randomized study of oral toceranib phosphate (SU11654), a receptor tyrosine kinase inhibitor, for the treatment of dogs with recurrent (either local or distant) mast cell tumor following surgical excision. Clin Cancer Res 15 (11), 3856-65 PubMed.
  • Murphy S, Sparkes A H, Blunden A S, Brearley M J & Smith K C (2006) Effects of stage and number of tumours on prognosis of dogs with cutaneous mast cell tumours. Vet Rec 158 (9), 287-291 PubMed.
  • Scase T J, Edwards D, Miller J, Henley W, Smith K, Blunden A & Murphy S (2006) Canine mast cell tumous: correlation of apoptosis and proliferation markers with prognosis. J Vet Intern Med 20 (1), 151-158 PubMed.
  • Sfiligoi G, Rassnick K M, Scarlett J M, Northrup N C & Gieger T L (2005) Outcome of dogs with mast cell tumors in the inguinal or perineal region versus other cutaneous locations: 124 cases (1990-2001). JAVMA 226 (8), 1368-1374 PubMed.
  • Murphy S, Sparkes A H, Smith K C, Blunden A S & Brearley M J (2004) Relationships between the histological grade of cutaneous mast cell tumours in dogs, their survival and the efficacy of surgical resection. Vet Rec 154 (24), 743 -746 PubMed.
  • Weisse C, Shofer F S & Sorenmo (2002) Recurrence rates and sites for grade II canine cutaneous mast cell tumors following complete surgical excision. JAAHA 38 (1), 71-73 PubMed.
  • Séguin B, Leibman N F, Bregazzi V S et al (2000) Clinical outcome of dogs with grade II mast cell tumors treated with surgery alone - 55 cases (1996-1999). JAVMA 218 (7), 1120-1123 PubMed.
  • Rassnick K M et al (1999) Treatment of canine mast cell tumors with CCNU (Lomustine). J Vet Intern Med 13 (6), 601-605 PubMed.
  • Thamm D H, Mauldin E A, Vail D M (1999) Prednisone and vinblastine chemotherapy for canine mast cell tumor - 41 cases (1992-1997). J Vet Intern Med 13 (5), 491-497 PubMed.
  • Gerritsen R J et al (1998) Multiagent chemotherapy for mast cell tumors in the dog. Vet Q 20 (1), 28-31 PubMed.
  • LaDue T et al (1998) Radiation therapy for incomplete resected canine mast cell tumors. Veterninary Radiology and Ultrasound 39 (1), 57-62 Wiley Online Library.
  • Lewis D T (1998) Life-threatening dermatoses in dogs. Comp Cont Ed Pract Vet 20 (3), 271-283 VetMedResource.
  • Frimberger A E et al (1997) Radiotherapy of incompletely resected, moderately differentiated mast cell tumors in the dog - 37 cases (1989-1993). JAAHA 33 (4), 320-324 PubMed.
  • al-Sarraf R et al (1996) A prospective study of radiation therapy for the treatment of grade 2 mast cell tumors in 32 dogs. J Vet Intern Med 10 (6), 376-378 PubMed.
  • Lemarié R J, Lemarié S L & Hedlund C S (1995) Mast cell tumors - clinical management. Comp Cont Ed Pract Vet 17 (9), 1085-1101 VetMedResource.
  • McCaw D L et al (1994) Response of canine mast cell tumors to treatment with oral prednisone. J Vet Intern Med 8 (6), 406-408 PubMed.
  • Grier R L, DiGuardo G, Schaffer C B et al (1990) Mast cell tumor destruction by deionized water. Am J Vet Res 51 (7), 1116-1120 PubMed.
  • Dean P W (1988) Mast cell tumors in dogs - diagnosis, treatment and prognosis. Vet Med 83 (2), 185-188 VetMedResource.
  • O'Keefe D A et al (1987) Systemic mastocytosis in 16 dogs. J Vet Intern Med 1 (2), 75-80 PubMed.
  • Patnaik A K et al (1984) Canine cutaneous mast cell tumor morphologic grading and survival in 83 dogs. Vet Pathol 21 (5), 469-474 PubMed.