JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

October 2016

I-N21

 

Signalment (JPC # 1957907):  Age and breed unspecified dog

HISTORY:  None

HISTOPATHOLOGIC DESCRIPTION (Slide A):  Haired skin and subcutis:  Infiltrating the dermis and subcutis, elevating the epidermis, separating and surrounding adnexa, skeletal muscle fibers and collagen bundles, and extending to the margins of the submitted tissue is an unencapsulated, poorly-circumscribed neoplasm composed of sheets of neoplastic mast cells.  Neoplastic cells are round with distinct cell borders, moderate amounts of amphophilic cytoplasm that occasionally contain fine basophilic granules, and generally centrally located, round nuclei with coarsely stippled chromatin and 1 to 2 variably distinct nucleoli.  The mitotic count averages 1 per 10 400X hpf.  Scattered throughout the neoplasm are moderate to high numbers of eosinophils and fewer lymphocytes, plasma cells, and hemosiderin-laden macrophages.  Multifocally, there are ectatic lymphatic vessels (edema) and blood vessels are congested. 

(Slide B) Luna mast cell stain:  Neoplastic cells contain numerous metachromatic granules.

MORPHOLOGIC DIAGNOSIS:  Haired skin and subcutis:  Mast cell tumor, low grade (grade II), breed unspecified, canine

Signalment (JPC # 2924576):  13-year-old standardbred gelding

HISTORY:  A subcutaneous mass on the right flank

HISTOPATHOLOGIC DESCRIPTION (Slide C):  Subcutis (per contributor):  Infiltrating, separating, and surrounding collagen bundles is an unencapsulated, poorly- circumscribed, relatively paucicellular neoplasm composed of sheets of neoplastic mast cells.  Neoplastic cells are round with distinct cell borders, moderate amounts of amphophilic cytoplasm that often contain fine basophilic granules, and centrally located, oval nuclei with coarsely stippled chromatin and indistinct nucleoli.  There is moderate anisocytosis and anisokaryosis.  The mitotic rate is 1 per 10 hpf.  There are multiple large, irregular, up to 5 mm diameter areas of necrosis composed of brightly eosinophilic cellular and karyorrhectic debris, neoplastic mast cells, and multifocal brightly eosinophilic, hyalinized bands of collagen (collagenolysis), that are bordered by deeply basophilic fragmented mineral, and dense fibrous connective tissue, admixed with fine, beaded amphophilic mucin, epithelioid macrophages, and multinucleated giant cells.  Scattered throughout the neoplasm, there is hemorrhage, moderate numbers of hemosiderin-laden macrophages, and occasional eosinophils.

MORPHOLOGIC DIAGNOSIS:  Subcutis (per contributor):  Mast cell tumor, standardbred, equine

SYNONYMS:  Mastocytoma, cutaneous mastocytosis

GENERAL DISCUSSION:

Normal Mast Cell Production and Function:

PATHOGENESIS:

TYPICAL CLINICAL FINDINGS:

Dogs:

Horses:

Subgroup of poorly differentiated equine cutaneous MCT in which aberrant KIT expression is associated with high proliferative rate and potential aggressive behavior Cats:

TYPICAL GROSS FINDINGS:

TYPICAL LIGHT MICROSCOPIC FINDINGS:

A Grenz zone is typically present; may be epitheliotropic

Horses:

Dogs:

Grading Systems:

 

  Grade 1

Grade 2

Grade 3

Differentiation

Well-differentiated; medium-sized; distinct granules

Moderate; fine, distinct granules

Poorly- differentiated;

indistinct or no granules

Nuclei

Monomorphic;

round, condensed chromatin; no nucleoli

Mild pleomorphism;

round to indented

scattered chromatin;

occasional nucleoli;

binucleated and giant cells

Large; pleomorphic; fine chromatin; 1 or more nucleoli;

binucleated and multinucleated giant cells are common

Mitotic index average/hpf

0/hpf

0-2/hpf

3-6/hpf

Penetration

Superficial dermis→ interfollicular

Deep dermis to SQ

SQ to deeper tissues

Aggressive features

None

Occasional edema; necrosis

Edema; necrosis common

 

Lymph node cytology:

ULTRASTRUCTURAL FINDINGS:

ADDITIONAL DIAGNOSTIC TESTS:

DIFFERENTIAL DIAGNOSIS:

Other round cell neoplasms (for grade III usually, since they are poorly differentiated):

Horse (for eosinophilic inflammation):

COMPARATIVE PATHOLOGY:

REFERENCES:

  1. Abbas AK, Aster JC, Kumar V, et. al. Diseases of the immune system. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Philadelphia, PA: Elsevier Saunders; 2015:202-204.
  2. Aresu L, Benali S, Giantin M, et. al. Expression of matrix metalloproteinases, tissue inhibitors of metalloproteinases and vascular endothelial growth factor in canine mast cell tumours. J Comp Path. 2012;147(4):419-429.
  3. Atherton MJ, Pratschke KM, Sillito JA, et. al. Evaluation of a modified proportional margins approach for surgical resection of mast cell tumors in dogs: 40 cases (2008-2012). J Am Vet Med Assoc. 2013;243(10):1436-1441.
  4. Bailey KL, Kiupel M, Webster JD, et. al. Proposal of a 2-tier histologic grading system for canine cutaneous mast cell tumors to more accurately predict biologic behavior. Vet Pathol. 2011;48(1):147-155.
  5. Berlto D, Bettini G, Sabattini S, Scarpa F. Histological Grading of Canine Mast Cell Tumor: Is 2 Better Than 3?, Vet Pathol. 2015 Jan;52(1):70-3
  6. Camus MS, Koehler JW, Priest HL, et. al. Cytologic criteria for mast cell tumor grading in dogs with evaluation of clinical outcome. Vet Pathol. 2016; DOI: 10.1177/0300985816638721.
  7. Campbell KL, Griffin CE, Miller WH. Neoplastic and non-neoplastic tumors. In: Scott DW, Miller WH, Griffin CE eds. Small Animal Dermatology. 7th ed. Philadelphia, PA: W.B. Saunders Company; 2013:806-810.
  8. Capello K, Giantin M, Vascellari M, et. al. Expression of Ki67, BCL-2, and COX-2 in canine cutaneous mast cell tumors: Association with grading and prognosis. Vet Pathol. 2013;50(1):110-121.
  9. Clarke L, Ehrhart EJ, Simon A, al. Histologic characteristics and KIT staining patterns of equine cutaneous mast cell tumors. Vet Pathol. 2014;51(3):560-2.
  10. Ehler WJ, MacEwen EG, Patnaik AK. Canine cutaneous mast cell tumor: Morphologic grading and survival time in 83 dogs. Vet Pathol. 1984;21(5):469-474.
  11. Elliott JW, Lewis BC, Oliveira FN. et. al. Cutaneous mast cell tumor with epitheliotropism in 3 dogs. Vet Pathol. 2013;50(2):234-237.
  12. Frizzon MG, Gentilini F, Sabattini S, et. al. Prognostic significance of Kit receptor tyrosine kinase dysregulations in feline cutaneous mast cell tumors. Vet Pathol. 2013;50(5):797-805.
  13. Goldschmidt MH, Hendrick MJ. Tumors of the skin and soft tissues. In: Tumors in Domestic Animals. 4th ed. Ames, IA: Iowa State Press; 2002:105-109.
  14. Gross TL, Ihrke PJ, Walder EJ. Mast cell tumors. In: Gross TL, Ihrke PJ, Walder EJ, Skin Diseases of the Dog and Cat. 2nd ed. Ames, IA: Blackwell Science Ltd; 2005:853-865.
  15. Gruber AD, Klopfleisch R, Meyer A. CD25 Is expressed by canine cutaneous mast cell tumors but not by cutaneous connective tissue mast cells. Vet Pathol. 2012;49(6):988-997.
  16. Hargis AM, Meyers S. The integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier Mosby; 2016:755, 1119, 1297, 1248.
  17. Hendrick MJ, Mahaffey EA, Moore FM, et al. Histologic Classification of Mesenchymal Tumors of Skin and Soft Tissues of Domestic Animals. 2nd series, Vol 2. Washington, DC: Armed Forces Institute of Pathology; 1998.
  18. Kipar A, Ressel L, Ward S. Equine Cutaneous Mast Cell Tumors Exhibit Variable Differentiation, Proliferation Activity and JIT Expression, J Comp Pathol. 2015 Nov; 153(4): 236-243
  19. Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Saunders Elsevier; 2016: 730-732.
  20. Morrison JA, Pearl DL, Thompson JJ, et. al. Receptor tyrosine kinase expression profiles in canine cutaneous and subcutaneous mast cell tumors. Vet Pathol. 2016;53(3):548-558.
  21. Pearl DL, Thompson JJ, Yager JA, et. al. Canine subcutaneous mast cell tumor: Characterization and prognostic indices. Vet Pathol. 2011;48(1):156-168.
  22. Scott DW. Neoplastic diseases. In: Scott DW, ed. Large Animal Dermatology. Philadelphia, PA: W.B. Saunders Company; 1988:441-444.
  23. Scott DW, Miller WH. Neoplastic and non-neoplastic tumors. In: Scott DW, Miller WH, eds. Equine Dermatology. St. Louis, MO: Saunders; 2003:746-753.


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