October 2016



Signalment (JPC# 2017869):  Horse

HISTORY:  This horse had a dermal mass

HISTOPATHOLOGIC DESCRIPTION (Slide A):  Haired skin:  Expanding and effacing the deep dermis, infiltrating the subcutis, elevating the epidermis, and extending to cut margins is an unencapsulated, well circumscribed, densely-cellular neoplasm composed of sheets of round cells on a moderate pre-existing collagenous stroma.  Neoplastic cells have indistinct cell borders, scant amount of eosinophilic cytoplasm, round to ovoid nuclei with finely stippled chromatin and 1-3 variably distinct nucleoli.  The mitotic count averages 1 per 40X HPF.  Admixed with neoplastic cells are many small, reactive lymphocytes and large histiocytes up to 20 um in diameter.  Histiocytes have moderate amounts of eosinophilic cytoplasm and are occasionally filled with variably sized, up to 1 x 7 um, eosinophilic acicular crystals.  There is multifocal individual cell necrosis.   

MORPHOLOGIC DIAGNOSIS:  Haired skin, site not specified:  Lymphoma, nonepitheliotropic, breed not specified, equine.

Signalment (JPC# 2604555):  Cow

HISTORY:  This cow had multiple, 1-3 cm diameter, cutaneous bumps.

HISTOPATHOLOGIC DESCRIPTION (Slide B):  Haired skinInfiltrating the dermis, separating and surrounding adnexa and pre-existing collagen bundles, elevating the focally eroded epidermis, and occasionally infiltrating the epidermis and follicular epithelium is an unencapsulated, poorly circumscribed, densely-cellular neoplasm composed of sheets of round cells.  Neoplastic cells have indistinct cell borders and scant eosinophilic granular cytoplasm.  Nuclei are round to ovoid with coarsely-stippled chromatin and 1-4 distinct nucleoli.  The mitotic count is up to 4 per HPF.  There is multifocal individual cell necrosis.  Multifocally, neoplastic cells infiltrate the follicular epithelium and epidermis forming Pautrier’s microabscesses.  Within the superficial dermis, there is multifocal moderate hemorrhage admixed with fibrin and edema.  Overlying the epidermis and occasionally extending into follicular lumina is a 500 um thick serocellular crust composed of many degenerate neutrophils admixed with abundant serum, necrotic debris, and multifocal colonies of 1 um diameter cocci.  Multifocal apocrine glands adjacent to the neoplasm are mildly ectatic.    

MORPHOLOGIC DIAGNOSIS:  Haired skin, site not specified:  Lymphoma, epitheliotropic, breed not specified, bovine.



Equine:  Malignant lymphoma is the most common malignant neoplasm of the horse; the quarter horse is the most common breed affected; there are two main forms:

Bovine:  Lymphoma is categorized by frequency of occurrence (sporadic or endemic/enzootic), age at onset, organ system(s) involved, and the etiologic agent:





Equine cutaneous lymphoma:

Bovine cutaneous lymphoma:


Equine cutaneous lymphoma:

Bovine cutaneous lymphoma:


Equine nonepitheliotropic (most commonly TCRBCL):

Equine epitheliotropic:

Bovine (cutaneous form):





Equine cutaneous lymphoma:

Bovine cutaneous lymphoma:




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