Title: Histiocytoma (dog)

{{Short description|Benign tumor in dogs}}
[[File:Progression of a histocytoma on a French bulldog ear.jpg|thumb|Progression of a Histocytoma on a French Bulldog Ear -2 months time]]
[[Image:Histiocytoma.JPG|thumb|A histiocytoma on the ear of a dog]]
[[Image:Canine histiocytoma.jpg|thumb|Canine Cutaneous Histiocytoma on a young boxer dog]]
A '''histiocytoma''' in the [[dog]] is a benign tumor.  It is an abnormal growth in the skin of [[histiocyte]]s ([[histiocytosis]]), a cell that is part of the [[immune system]].  A similar disease in humans, [[Hashimoto-Pritzker disease]], is also a [[Langerhans cell histiocytosis]].&lt;ref&gt;{{cite journal |vauthors=Marchal T, Saint-André I, Magnol J, Dezutter-Dambuyant C, Schmitt D |title=[Dendritic cells in dogs and cats: models of study in human pathology] |journal=Pathol. Biol. |volume=43 |issue=10 |pages=910–20 |year=1995 |pmid=8786898}}&lt;/ref&gt;  Dog breeds that may be more at risk for this tumor include [[Bulldog]]s, American Pit Bull Terriers, American Staffordshire Terriers, [[Scottish Terrier]]s, [[Greyhound]]s, [[Boxer (dog)|Boxer]]s, and [[Boston Terrier]]s.  They also rarely occur in [[goat]]s and [[cattle]].&lt;ref&gt;{{cite web | title = Tumors with Histiocytic Differentiation | work = The Merck Veterinary Manual | year = 2006 | url = http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/72232.htm | accessdate = 2007-04-29 }}&lt;/ref&gt;

==Histiocytic disorders==
A histiocyte is a differentiated tissue cell that has its origin in the [[bone marrow]].  The source for histiocytes is the [[monocyte]]/[[macrophage]] line.  Monocytes (found in the blood) and macrophages (found in tissue) are responsible for [[phagocytosis]] (ingestion) of foreign material in the body.  [[Langerhans cell]]s are [[dendritic cell]]s found in the skin and function by internalizing [[antigen]]s (foreign particles) and presenting them to [[T cell]]s.  They arise from monocytes.&lt;ref&gt;{{cite journal |vauthors=Ginhoux F, Tacke F, Angeli V, Bogunovic M, Loubeau M, Dai XM, Stanley ER, Randolph GJ, Merad M |title=Langerhans cells arise from monocytes ''in vivo'' |journal=Nat. Immunol. |volume=7 |issue=3 |pages=265–73 |year=2006 |pmid=16444257 |doi=10.1038/ni1307|pmc=4727824 }}&lt;/ref&gt;  Histiocytic disorders refer to diseases that are caused by abnormal behavior of these cells.  They include the following:
*Reactive diseases of Langerhans cells
**Histiocytomas
**Cutaneous histiocytosis
**Systemic histiocytosis
*Reactive diseases of macrophages
**[[Hemophagocytic syndrome]] - a condition where macrophages phagocytose [[myeloid]] and [[erythroid]] precursors (similar to [[HLH (Hemophagocytic lymphohistiocytosis)|hemophagocytic lymphohistiocytosis]] in humans)
*Malignant diseases of Langerhans cells
**[[Malignant histiocytosis]] - a condition found in [[Bernese Mountain Dog]]s
**[[Diffuse histiocytic sarcoma]]
**Localized histiocytic sarcoma
*Malignant diseases of macrophages 
**[[Histiocytic lymphoma]]

==Tumor biology==
[[Image:Canine histiocytoma cytology.JPG|thumb|Canine histiocytoma cytology]]
A histiocytoma originates from epidermal Langerhans cells of [[antigen-presenting cell]] lineage.&lt;ref&gt;{{cite journal |vauthors=Moore P, Schrenzel M, Affolter V, Olivry T, Naydan D |title=Canine cutaneous histiocytoma is an epidermotropic Langerhans cell histiocytosis that expresses CD1 and specific beta 2-integrin molecules |journal=Am. J. Pathol. |volume=148 |issue=5 |pages=1699–708 |year=1996 |pmid=8623937 |pmc=1861573}}&lt;/ref&gt;  Spontaneous regression is common in these tumors, and it is mediated by infiltration of [[CD8]]-expressing T cells followed by expression of Type 1 [[T helper cell]] [[cytokine]]s (such as [[Interferon-gamma]]) and recruitment of antitumour [[effector cell]]s.&lt;ref&gt;{{cite journal |vauthors=Kaim U, Moritz A, Failing K, Baumgärtner W |title=The regression of a canine Langerhans cell tumour is associated with increased expression of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA |journal=Immunology |volume=118 |issue=4 |pages=472–82 |year=2006 |pmid=16764690 |doi=10.1111/j.1365-2567.2006.02394.x |pmc=1782326}}&lt;/ref&gt;

==Symptoms==
Most commonly histiocytomas are found in young dogs and appear as a small, solitary, hairless lump,&lt;ref name=Morrison_1998&gt;{{cite book|author=Morrison, Wallace B.|title=Cancer in Dogs and Cats|url=https://archive.org/details/cancerindogscats0000morr|url-access=registration|edition=1st|publisher=Williams and Wilkins|year=1998|isbn=0-683-06105-4}}&lt;/ref&gt;  although [[Shar Pei]]s may be predisposed to multiple histiocytomas.&lt;ref name=DVM&gt;{{cite journal | last = Cronin | first = Kim | title = Deciphering the histiocytic code | journal = DVM | pages = 1S–8S | publisher = Advanstar Communications | date = Dec 2006 }}&lt;/ref&gt;  They are most commonly found on the head, neck, ears, and limbs, and are usually less than 2.5&amp;nbsp;cm in diameter.&lt;ref&gt;{{cite web | last = Affolter | first = Verena K. | title = Histiocytic Proliferative Diseases in Dogs and Cats | work = Proceedings of the 29th World Congress of the World Small Animal Veterinary Association | year = 2004 | url = http://www.vin.com/proceedings/Proceedings.plx?CID=WSAVA2004&amp;PID=8600&amp;O=Generic | accessdate = 2007-04-29 }}&lt;/ref&gt;  Ulceration of the mass is common.  Diagnosis is made through [[cytopathology|cytology]] of the mass.  Cytology reveals cells with clear to lightly [[basophilic]] [[cytoplasm]] and round or indented [[cell nucleus|nuclei]] with fine [[chromatin]] and indistinct [[nucleolus|nucleoli]].&lt;ref&gt;{{cite web | last = Raskin | first = R.E. |author2=DeNicola, D. | title = Cytology of Neoplasia | work = Proceedings of the North American Veterinary Conference | year = 2006 | url = http://www.ivis.org/proceedings/NAVC/2006/SAE/105.asp?LA=1 | accessdate = 2007-04-29 }}&lt;/ref&gt;

==Treatment==
Most histiocytomas will regress within two or three months.&lt;ref name=Morrison_1998/&gt;  Histiocytomas can regress and disappear completely using antihistamine medications: H1 antagonist is diphenhydramine (Benadryl), and/or the H2 antagonist famotidine (Pepsid). Histiocyte growth can be suppressed  using either or both of the H1/H2 antagonists.  This can be curative. Surgical removal may be necessary if the tumor does not regress or if it is growing rapidly to a large size.  Histiocytomas should never be treated with an intralesional injection of a [[corticosteroid]], as remission relies on recognition of the tumour by the body's immune system which is suppressed by steroids.

==References==
{{Reflist}}

==External links==
*[http://www.veterinarypartner.com/Content.plx?P=A&amp;S=0&amp;C=0&amp;A=1676 ''Histiocytoma'' from The Pet Health Library]
*[http://www.petcancercenter.org/Cancer_Types_soft_tissue_histiocytic_sarcoma.html ''Histiocytoma and Histiocytic Sarcoma in Cats and Dogs'' from Pet Cancer Center]
*[http://www.xs4all.nl/~gvdt57/usa/histiocytoma_farley.html Photos of histiocytoma in a Shetland Sheepdog (Sheltie)]

[[Category:Dog diseases]]