Signalment:  

8-year-old intact female Golden Retriever dog, Canis familiars.A female, golden retriever dog presented for abnormality in the left eye. The intraocular proliferative lesion was confirmed by ultrasonography. No other symptoms were found at clinical examination. Because tumor lesion was suspected in globe, left eye enucleation was performed.

Gross Description:  

The left eye was swollen and approximately 2.5 cm in diameter. The lesion was mainly located in the anterior and posterior uvea and was gray-white or black in color. The lens was dislocated in the globe. The optic nerve had no remarkable change.

Histopathologic Description:

The neoplastic tissue effaced the iris and choroid in the globe and was composed of large pleomorphic mononuclear cells and multinucleated giant cells. In addition, some lesions include spindle cell forms, which resemble spindle cell sarcomas such as malignant melanoma. The tumor cells were loosely arranged in sheets, and were partially dispersed. Neutrophils multifocally infiltrated the neoplasm, and there were areas of necrosis and hemorrhage. Tumor cells were predominantly mononuclear cells with marked pleomorphism. The cytoplasm was eosinophilic and varied from scant to abundant. Cytoplasmic vacuolation was frequently encountered. Nuclei were ovoid, indented or folded and extremely variable in size. The chromatin pattern was coarsely granular. Nucleoli were large and frequently multiple. The mitotic index was high and bizarre mitotic figures were frequently shown. Tumor cells often engulfed erythrocytes, melanin granules, nutrophils and mononuclear cells such as lymphocytes. These tumor cells were moderately immunoreactive with Iba-1, lysozyme, MHC-class II and vimentin. However, tumor cells were negative for cytokeratin AE1/AE3, CD3, CD18, CD20, CD79cy, E-cadherin, Melan-A, neurofilament, and S-100 protein. In electron microscopy, the predominant large irregular cells with abundant cytoplasm had no discernable junctional complexes or basal lamina. The cytoplasm contained numerous organelles, including rough endoplasmic reticulum, and a prominent Golgi apparatus. Mitochondria varied in size and shape. However, the number of lysosomes was small, and phagolysosomes and secondary lysosomes were sometimes seen. Tumor cells also contained small lipid droplets.

Morphologic Diagnosis:  

Eye: Histiocytic sarcoma.

Condition:  

Histiocytic sarcoma

Contributor Comment:  

The initial presentation of our case is an intraocular lesion. The first presenting sign is an ocular abnormality with no other apparent proliferative lesions in clinical examination. After one month, a contralateral globe lesion and disseminated cutaneous masses, which are also diagnosed as histiocytic sarcoma, are identified. Because histiocytic sarcoma is capable of widespread metastasis, it is not always possible to differentiate true multicentric origin as malignant histiocytosis from widespread metastasis of disseminated histiocytic sarcoma. However, as the lesions of eye and cutis do not occur simultaneously and the ocular neoplasm is firstly recognized, our case can be regarded as disseminated histiocytic sarcoma likely to be intraocular in origin.

Histiocytic sarcoma, which is identified as a single lesion of histiocytic neoplasia, is due to proliferation of dendritic antigen presenting cells (DC). The majority occurs in the subcutis, but other primary locations have been observed. Disseminated histiocytic sarcoma, which spreads to distant sites beyond the local lymph nodes, is an aggressive multisystem disease characterized by presence of multiple tumor masses in several organ systems. Primary sites are spleen, lung, and bone marrow. Secondly, lesions are observed in lymph nodes and liver, and subsequently other organs can be affected. When histiocytic neoplasia occurs in multiple sites simultaneously, the disease is termed malignant histiocytosis.(1)

Histiocytic sarcoma is an uncommon primary intraocular neoplasm, whereas life expectancy following diagnosis is very short compared to other ocular tumors. It is important that malignant melanoma, irido-ciliary epithelial tumor, and malignant lymphoma were eliminated from the differential diagnosis by histomorphologic examination. Melanocytic tumors arising from the uvea are the most commonly detected ocular tumors in dogs, and approximately 20% of these tumors are malignant melanoma. Irido-ciliary epithelial tumor is the second-most-common primary uveal tumor in dogs, accounting 12.5% of canine ocular tumors. Primary malignant lymphoma is the third-most-common intraocular tumor in dogs, representing 3.3% of canine ocular tumors.(9)

Primary intraocular histiocytic sarcoma has a strong breed association. Approximately 70% of these tumors occur in Retriever breeds accounting for Golden Retrievers and Labrador Retrievers.(9) Among other breeds Rottweilers are the third-most-common breed. On the other hand, histiocytic sarcoma and malignant histiocytosis is best recognized in the Bernese mountain dog, in which a familial association is apparent.(5) Other breeds are predisposed to histiocytic sarcoma and include Rottweilers, Golden Retrievers, and Flat-coated Retrievers. Because histiocytic sarcoma is characterized by rapid dissemination, it should be listed in differential diagnoses of intraocular tumors of Retriever breeds, especially Golden Retrievers and Labrador Retrievers.

Histiocytes differentiate from CD34+ myeloid stem cells into monocyte/macrophages and several dendritic antigen presenting cells (DC) lineages, which include epithelial DC or Langerhans cells, interstitial DC, plasmacytoid DC, and interdigitating DC of the paracortical area of the lymph node. Histiocytic sarcomas express leukocyte surface molecules characteristic of DC such as CD1, CD11c and MHC II.(1) Diffuse expression of E-cadherin, CD4 and Thy-1 has not been observed in histiocytic sarcoma. On the other hand, the phenotype of histiocytoma, which is a benign tumor of non-activated Langerhans cells, is quite similar to that of histiocytic sarcoma except for the expression of E-cadherin, which occurs in histiocytoma especially in the cellular infiltrate immediately adjacent to the epidermis. Reactive histiocytosis, which is a proliferative disease of activated interstitial DC, consistently expresses CD4 and Thy-1.(1)

CD1, CD11c and CD4 antibodies could not be used on formalin fixed paraffin embedded specimens. So, we need to use the antibody panel for CD3 (T cells), CD20 (B cells), CD79cy (B cells), CD18 (macrophage, lymphocyte, granulocyte), MHC-II, Iba-1 (macrophage, microglia). MHC-II, Iba-1 and lysozyme expression with the absence of CD3, CD20 and CD79cy is evidence of macrophage and DC differentiation. Macrophages, which are specialized scavengers, have more numerous lysosomes than dendritic antigen presenting cell (DC). In the present case, the neoplastic cells have small numbers of lysosomes under electron microscopic examination. Thus, these neoplastic cells are regarded as DC rather than macrophages. In addition, neoplastic cells are negative for E-cadherin, which intra-epithelial DC such as Langerhans cells express. The exact sublineages of histiocytes and dendritic cells involved in HS have not been determined in most instances, but our present case is highly suggestive of interstitial DC origin.

JPC Diagnosis:  

Eye: Histiocytic sarcoma.

Conference Comment:  

The contributor provides an excellent overview of histiocytic proliferative diseases. Curiously, this neoplasm is negative for CD18, a β2-integrin subunit expressed by all leukocytes including histiocytes, dendritic cells, lymphocytes and granulocytes. In a recent article differentiating ocular histiocytic sarcoma from melanocytic neoplasms(10), all neoplasms considered to be histiocytic sarcoma were either Melan A and/or S-100 protein negative and/or CD18 positive. Additionally, this neoplasm demonstrates immunoreactivity for MHCII and Iba-1, an ionized calcium-binding adaptor specific for macrophages and microglia. Via electron microscopy, only a few lysosomes and phagosomes were identified, suggesting this neoplasm is possibly of myeloid dendritic cell origin rather than macrophage. The immunophenotyping of cells throughout the spectrum of histiocytic diseases varies based on the reference text or journal consulted, and reflects the continuous information explosion in this very active field of research. The following list outlines the most consistent and commonly cited immunophenotypes(1-8):

Cell of origin	Disease(s)	Immunohistochemistry
		Positive	Negative
Epidermal dendritic (Langerhans) cell	Cutaneous histiocytoma; Feline PCLH (Birbecks granules on EM)	E-cadherin, CD1a, CD14, CD11c, CD18, MHC II, ICAM-1, langerin	Thy-1, CD4
Interstitial dendritic cell	Reactive histiocytosis	Thy-1, CD4, CD1c, CD11b/c, MHC II, CD18	ICAM-1, E-cadherin
Myeloid dendritic cell	Histiocytic sarcoma	ICAM-1, CD1, CD11c, MHC II, -� CD90	CD4, E-cadherin
Macrophage	Hemophagocytic histiocytic sarcoma	CD11d (β2- integrin), MHC II, -� CD11c/CD18, CD1c	CD1c/CD11c

References:

1. Affolter V, Moore PF. Localized and disseminated histiocytic sarcoma of dendritic cell origin in dogs. Veterinary Pathology. 2002;39:74.
2. Affolter VK, Moore PF. Canine cutaneous and systemic histiocytosis. Am J Dermatopathol. 2000;22:40-48.
3. Baines SJ, McInnes EF, McConnell I. E-cadherin expression in canine cutaneous histiocytomas. Vet Rec. 2008;162(16):509-513. 
4. Coomer AR, Liptak JM. Canine histiocytic diseases. Compend Contin Educ Vet. 2008;30(4):202-204.
5. Dubielzig RR, Ketring KL, McLellan GJ, et al. Uveal neoplasia. Veterinary ocular pathology. Philadelphia, PA: Saunders; 2010:282-309.
6. Fernandez NJ, West KH, Jackson ML, et al. Immunohistochemical and histochemical stains for differentiating canine cutaneous round cell tumors. Vet Pathol. 2005;42(4):437-445.
7. Ginn PE, Mansell JEKL, Rakich PM. Skin and appendages. In: Maxie MG, ed. Jubb, Kennedy, and Palmer's Pathology of Domestic Animals 5th ed. vol. 1. Philadelphia, PA: Saunders Elsevier; 2007:768-769.
8. Goldschmidt MH, Hendrick MJ. Tumors of the skin and soft tissues. In: Meuten DJ, ed. Tumors in Domestic Animals. 4th ed. Ames, IA: Iowa State Press; 2002:109-111.
9. Moore PF, Rosin A. Malignant histiocytosis of Bernese mountain dogs. Vet Pathol. 1986:23:1-10.
10. Naranjo C, Dubielzig RR, Friedrichs KR. Canine ocular histiocytic sarcoma. Vet Ophthalmol. 2007 May-Jun;10(3):179-85.

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