Primary Splenic Leiomyosarcoma With Metastasis in a Rhesus Monkey (Macaca mulatta)

ABSTRACT

Primary mesenchymal tumours of the spleen in non‐human primates are exceedingly rare. We report on a 13‐year‐old female rhesus monkey who had an enlarged liver, spleen and multiple lung masses. Macroscopic, microscopic and immunohistochemical examinations revealed a splenic leiomyosarcoma with widespread metastasis. This is the first report of a splenic leiomyosarcoma in a non‐human primate.

Primary mesenchymal tumours of the spleen in non‐human primates are exceedingly rare. We report on a 13‐year‐old female rhesus monkey who had an enlarged liver, spleen and multiple lung masses. Macroscopic, microscopic and immunohistochemical examinations revealed a splenic leiomyosarcoma with widespread metastasis. This is the first report of a splenic leiomyosarcoma in a non‐human primate

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1. Introduction

Smooth muscle is found in large quantities in the digestive and urogenital tracts. Tumours arising from smooth muscle have been diagnosed in domestic as well as laboratory animals, including non‐human primates. In non‐human primates, leiomyomas or leiomyosarcomas have been identified in the uterus (Macaca mulatta (McClure 1973; Cook et al. 2004; Jackson 1996; Takayama et al. 2000; McClure 1980; Beniashvilli 1989; Seibold and Wolf 1973), Papio spp. (Cianciolo and Hubbard 2005; Beniashvilli 1989), Macaca fascicularis (Takayama et al. 2000; Kaspareit et al. 2007; Wilkinson et al. 2008), Pan troglodytes (Beniashvilli 1989; Seibold and Wolf 1973), Macaca nemestrina (Birkebak et al. 1996), Macaca fuscata (Gall et al. 2018), Callithrix spp. (Beniashvilli 1989), Chlorocebus spp. (Beniashvilli 1989)), subcutis (Macaca fascicularis, Saimiri sciureus (Nakamura et al. 2010; Brunnert et al. 1990)), esophagus (Macaca fascicularis) (Kaspareit et al. 2007), stomach (Macaca mulatta) (Beniashvilli 1989; Lowenstine 1986), small intestine (Macaca mulatta (Bradfield et al. 1995), Macaca nigra (Aristizabal‐Arbelaez et al. 2012)), colon (Macaca mulatta (Lowenstine 1986; Bunton and Bacmeister 1989), Galagoides demidovii (Brack 1998), Saguinus Oedipus (Brack 1998)) and hind limb (Macaca cyclopis (Kim et al. 2009)). A single case of metastatic leiomyosarcoma with unknown origin has been reported in Macaca arctoides (Lowenstine 1986). The spleen is an organ that is often diagnosed with primary vascular or lymphoid neoplasms. Other intrinsic neoplasms include nervous, fibrous and smooth muscle. Smooth muscle tumours involving the spleen are rare in humans (Daudia et al. 2001; Piovanello et al. 2007; Oguzkurt et al. 1996; Shapochnik et al. 2010; Pletinchx et al. 2007) and domestic animals, except for the dog. To the author's knowledge, there have been no reports of splenic leiomyosarcoma in non‐human primates.

2. Materials and Methods

2.1. Humane Care Guidelines

The animal subject of this report was maintained in an AAALAC International‐accredited animal facility and was part of a study approved by the Institutional Animal Care and Use Committee. The study was conducted in a public health service‐assured institution in accordance with current guidelines for animal welfare.

A 13‐year‐old, 4 kg female rhesus monkey (Macaca mulatta) was reported for intermittent coughing. The animal was sedated. A mild dry cough was induced when changing her position. On physical examination, a large mass was palpable in the left cranial abdomen adjacent to the last ribs. Radiographs of her chest and abdomen were obtained and yielded a military lung pattern and enlarged liver. Because of her decreased abdominal adipose content, the contrast was poor for any further evaluation. Because of radiographic findings, the decision to euthanize was elected. The animal was humanely euthanized with pentobarbital and then submitted for necropsy.

3. Results

At necropsy, the animal was in good nutritional condition with adequate hydration. The spleen was composed primarily of a lobulated mass that measured approximately 8 cm × 7 cm × 5 cm (Figure 1). The cut surface of these lobulations was pale tan with areas of necrosis and suspected blood clots. The liver was approximately twice the normal size and orange–brown in colour. Cutting into the liver revealed multifocal to coalescing varying‐sized masses, which ranged from pale tan to yellow to dark red–black in colour. The lungs contained multiple small tan‐brown to dark red–black masses throughout all lobes. Multiple tissues were collected and fixed in 10% neutral buffered formalin, routinely processed, embedded in paraffin, sectioned at 5 µm, and stained with haematoxylin and eosin.

FIGURE 1.

A large mass arises from the body of the spleen (S).

The masses in the spleen, liver and lungs were composed of moderately to markedly anisocytotic and anisokaryotic round to polygonal neoplastic cells with prominent cell borders, round to oval nuclei and finely stippled to coarsely clumped chromatin (Figure 2A). One to two varying‐sized round nucleoli were seen. The cytoplasm of the cells was eosinophilic and fibrillar, and a 1:1 to 2:1 nuclear:cytoplasmic ratio was observed. There were occasional randomly scattered giant neoplastic cells, and mitotic count per 2.4 mm² averaged 1. The cells were clustered into large individual coalescing masses and separated by a fine to dense fibrovascular network. There were large areas of telangiectasia, haemorrhage and small areas of necrosis. The masses were well‐circumscribed and partially encapsulated with tumour cells in the capsule and within the vascular lumen. A few small clusters of neoplastic cells were observed in the vasculature of a few coronary arteries and within small blood vessels of the adrenal gland capsule. A definitive diagnosis could not be made given the morphology of the cells, so immunohistochemistry was implemented.

FIGURE 2.

(A) Haematoxylin and eosin (H&E) stained, a highly cellular section of the tumour showing round to polygonal cells with mild to moderate anisocytosis and anisokaryosis. Immunohistochemical staining of tumour tissue for alpha‐smooth muscle actin, desmin and vimentin. (B) Alpha‐smooth muscle actin stains neoplastic cells strongly and diffusely, indicating smooth muscle origin. (C) Desmin staining is scattered and mild to moderate, indicating a muscle origin. (D) Vimentin stains sporadically, indicating mesenchymal differentiation. Scale 20 µm.

Immunohistochemical staining for factor VIII, CD3, Ham56, CD79a, S‐100, chromogranin, vimentin, pan‐cytokeratin (AE1/AE3), desmin and alpha‐smooth muscle actin was performed. Details of the antibodies utilized are shown in Table 1. Briefly, slides were deparaffinized, exposed to heat retrieval and primary antibodies were applied, followed by HRP‐bound secondary antibodies and chromogen Diaminobenzidine (BDB2004L, Biocare). Negative controls were made by eliminating the primary antibodies.

TABLE 1.

Immunohistochemistry antibody dilutions and clone information.

Target protein	Primary antibody	Dilution	Clone	Catalogue #	Company
αSMA	Mouse anti‐human, monoclonal antibody	1:100	1A4/asm‐1	NBP1‐30894	Novus
Desmin	Mouse anti‐human, monoclonal antibody	1:25	D33	16520‐1‐AP	Proteintech
Vimentin	Rabbit anti‐human, monoclonal antibody	1:100	Vim 3B4	5741S	Cell Signalling Technology
Factor VIII	Rabbit anti‐human polyclonal antibody	1:200	Factor VIII	CP0398	Biocare
CD3	Rabbit anti‐human, polyclonal antibody	1:600	CD3 epsilon	A0452	DAKO
Ham56	Mouse monoclonal antibody	1:50	Ham56	279M	Cell Marque
S‐100	Rabbit anti‐human polyclonal antibody	1:3000	S100B	Z0311	DAKO
Pan‐cytokeratin	Mouse anti‐human, monoclonal antibody	1:100	AE1/AE3	CM011B	Biocare
Chromogranin	Rabbit anti‐bovine polyclonal antibody	1:3000	SP‐1	20085	Immunostar, Inc.
CD79a	Mouse anti‐human, monoclonal antibody	1:100	JCB117	M7050	DAKO

Abbreviation: αSMA, alpha‐smooth muscle actin.

Strong diffuse cytoplasmic staining for alpha‐smooth muscle actin (Figure 2B), scattered mild to moderate cytoplasmic staining for desmin (Figure 2C), sporadic mild cytoplasmic staining for vimentin (Figure 2D) and negative staining for the remaining antibodies (data not shown) in the spleen, liver and lungs were characteristic of a leiomyosarcoma. Given the round to polygonal histomorphology of the cells, a final diagnosis of an epithelioid leiomyosarcoma was made.

Given the localized nature and size of the neoplastic tissue in the spleen, this tissue was determined to be the primary site of origin.

Splenic neoplasms in animals are primarily angiomatous and lymphomatous (Sangiorgio and Arber 2020; Linden et al. 2019). Interestingly, dogs have a high incidence of leiomyosarcomas of the spleen (Kapatkin et al. 1992; Spangler et al. 1994; Weinstein et al. 1989; Linden et al. 2019), while in other animal species, it is extremely rare (Feldman 1928). In humans, there are only a few case reports of primary smooth muscle neoplasms in the spleen (Daudia et al. 2001; Piovanello et al. 2007; Oguzkurt et al. 1996; Shapochnik et al. 2010; Pletinchx et al. 2007; Isaacson 1997; Monforte‐Munoz et al. 2003). The aetiology is mostly unknown; however Epstein–Barr Virus has been associated with smooth muscle neoplasms in immunocompromised humans (HIV, transplants), which most commonly arise in the lungs, liver and gastrointestinal tract (Barbashina et al. 2000)

A correct diagnosis of malignancy is usually made at a late stage, with frequent metastatic spread to the liver, lungs, bone, skin, brain and soft tissue (Piovanello et al. 2007).

Primary mesenchymal neoplasm of the spleen in non‐human primates is exceedingly rare. A single case report of a splenic angioleiomyoma has been described in an owl monkey (Aotus nancymae) (Gozalo et al. 2010), and a splenic haemangioma was described in a chacma baboon (Papio ursinus) (Cianciolo and Hubbard 2005).

Vascular smooth muscle is present in all tissue, including the spleen (Gozalo et al. 2010; Linden et al. 2019; Eberle et al. 2012), and is thought to be the primary site for smooth muscle tumours to arise (Akhaladze et al. 2019; Gage et al. 2012; Patrono et al. 2014; Rohde et al. 2001). However, the spleen also has smooth muscle trabeculae, which could have given rise to this neoplasm.

Leiomyosarcomas are non‐encapsulated, frequently invasive tumours which demonstrate malignant phenotypes such as pleomorphic spindle‐shaped or ovoid to round cells, high mitotic index, necrosis, haemorrhage and metastasis.

The human literature differentiates leiomyosarcomas into conventional (spindle cells), epithelioid and myxoid (Pinto 2024).

In humans, epithelioid leiomyosarcomas require the presence of unequivocal epithelioid morphology, that is, round to polygonal cells with eosinophilic cytoplasm and round to oval nuclei comprising more than 50% of the neoplasm (Chapel et al. 2022). In our case, the predominant cell type was epithelioid.

The diagnosis of this type of tumour is difficult owing to the morphology of the cells. Round cell tumours such as T‐cell lymphoma (CD3 negative), B‐cell lymphoma (CD79a negative), histiocytic sarcoma (Ham56 negative), neuroendocrine tumours (chromogranin negative), endothelial tumours like hemangiosarcoma (factor VIII negative), melanoma (S100 negative), peripheral nerve sheath tumour (S100 negative), rhabdomyosarcoma (SMA positive) and epithelial tumours (pan‐cytokeratin negative) were ruled out based on immunohistological results.

To the best of the author's knowledge, this is the first report of a primary splenic leiomyosarcoma with metastasis in a non‐human primate.

Author Contributions

Matthew F. Starost: conceptualization, investigation, writing – original draft, methodology, validation, visualization, writing – review and editing.

Ethics Statement

The animal subject of this report was maintained in an AAALAC International‐accredited animal facility and was part of a study approved by the Institutional Animal Care and Use Committee. The study was conducted in a Public Health Service Assured institution in accordance with current guidelines for animal welfare.

Conflicts of Interest

The author declares no conflicts of interest.

Peer Review

The peer review history for this article is available at https://www.webofscience.com/api/gateway/wos/peer‐review/10.1002/vms3.70378.

Data Availability Statement

The author is open to sharing all data.