History

A 2-year-old 147-g male intact longhaired Syrian hamster (Mesocricetus auratus) was presented for an evaluation of a mass on the ventral neck. The mass was first noticed 3 days prior to the reported physical evaluation.

Clinical and Clinicopathological Findings

Upon physical examination, a nonpainful, multilobulated, movable subcutaneous mass was present on the ventral neck. The mass measured approximately 24 X 12 mm. A fine-needle aspirate of the mass was collected for cytology. The sample was highly cellular and populated largely by individualized round cells (Figure 1). These cells had eccentrically located round nuclei, stippled to clumped chromatin, and variably sized nucleoli. Their cytoplasm was deeply basophilic and often contained a zone of paranuclear cytoplasmic clearing, with mild to moderate variability in nuclear-to-cytoplasmic ratio. Moderate to rarely marked anisocytosis with mild to moderate anisokaryosis were identified, as well as many binucleated or multinucleated cells. Rare mitotic figures and few small lymphocytes were appreciated.

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Photomicrographs of a fine-needle aspirate specimen obtained from a ventral neck mass in a 2-year-old intact male Syrian hamster (Mesocricetus auratus). A—The sample is highly cellular with minimal amounts of blood. Cells are arranged individually and in dense aggregates. Wright-Giemsa stain; 10X objective. B—A neoplastic round cell population is present. Cells have a plasmacytoid appearance with eccentrically located round nuclei, stippled to clumped chromatin, and a large amount of deep blue cytoplasm with a zone of paranuclear cytoplasmic clearing. Significant anisocytosis and anisokaryosis with occasional binucleation are apparent.

Citation: Journal of the American Veterinary Medical Association 2025; 10.2460/javma.24.08.0540

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Ten days after the initial presentation to the emergency service, the hamster was sedated with subcutaneous buprenorphine and an isoflurane gas mask, and an excisional biopsy was performed. Given the proximity of the mass to major vessels, the mass was narrowly excised, and the biopsy was submitted for a histopathologic evaluation. The patient was treated with meloxicam (0.1 mL of 1.5-mg/mL solution, PO) that was prescribed for at-home administration.

Histopathologic Findings

The excisional biopsy of a 24 X 12 X 12-mm lesion was trimmed, routinely processed, and stained with H&E for histopathologic evaluation. The tumor assessment revealed densely packed cellular sheets of plasmacytoid round cells affecting and infiltrating adipocyte lobules and salivary acini (Figure 2). Neoplastic cell nuclei were round to oval with eccentric and euchromatic reticular chromatin. A moderate amount of eosinophilic to amphophilic cytoplasm with some perinuclear clear zones or circular cytoplasmic packets was observed in the neoplastic cells. Scattered cells were abnormally large, and multinucleated or giant multilobulated nucleus was observed, in addition to a moderate anisocytosis and anisokaryosis as well as low mitotic index (0 or 1 mitotic figure/2.37-mm² field). Even though the lesion appeared completely excised, parts of the specimen margins were thin (< 1 mm).

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Photomicrograph of an excisional biopsy specimen from the lesion and patient described in Figure 1. The lesion consists of densely cellular sheets and packets of plasmacytoid round cells with delicate fibrovascular stroma and entrapped salivary acini (arrow). The plasmacytoid cells have a moderate amount of amphophilic cytoplasm with an eosinophilic perinuclear clear zone or a circular cytoplasmic packet. Nuclei are round to oval, central or eccentric, and euchromatic with reticulated chromatin. Scattered cells are abnormally large with multiple nuclei or a giant multilobulated nucleus. Mitotic index is low. H&E stain; bar = 25 µm.

Citation: Journal of the American Veterinary Medical Association 2025; 10.2460/javma.24.08.0540

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Morphologic Diagnosis and Case Summary

Salivary extramedullary plasmacytoma in a captive longhaired Syrian hamster.

Comments

Neoplastic diseases in pet hamsters are considered to occur relatively frequently despite few scientific reports in the current literature, most of which are based mainly on laboratory animals, rather than domestic hamsters.¹ A retrospective study of spontaneous tumors in pet hamsters from Japan found more tumors in females versus males, as well as a median age of 19.8 months.² Significant differences between Djungarian hamsters (Phodopus sungorus, aka Siberian hamsters or dwarf hamsters) and Syrian hamsters (Mesocricetus auratus) were also noted in this study. The Djungarian hamsters were almost exclusively affected by integumental neoplasms, mainly mammary tumors in females and papilloma or atypical fibromas in males. Syrian hamsters showed a much lower prevalence of neoplasia compared to the Djungarian hamsters, similar to historical reports in laboratory hamsters. Most Syrian hamsters in this study had hematopoietic neoplasms, with lymphoma and plasmacytoma being most common.² However, a more recent retrospective study of neoplasms in pet hamsters in Germany reported a younger median age of 12 months and did not find a significant sex predilection. Furthermore, Syrian hamsters more commonly presented with integumentary neoplasms in this study followed by hematopoietic tumors. No plasmacytomas were reported in this study.¹ Given these discrepancies, additional studies to account for potential geographic and species differences are warranted.

Plasmacytoma refers to a neoplastic process originating from mature, differentiated B lymphocytes. Extramedullary plasmacytomas in veterinary species are best characterized in cats and dogs. They are usually benign and can be found as solitary tumors in the skin, subcutis, or gastrointestinal tracts, with minimal recurrence after complete surgical excision. They are differentiated from multiple myeloma (dogs) or myeloma-related disorders (cats) based on the absence of bone involvement, lack of monoclonal immunoglobulin production, and typical absence of systemic illness. An interesting feature of this case is the salivary gland origin, which has been reported in 1 dog and is a rare finding in humans.³ While very rare in other species, multiple reports of salivary extramedullary plasmacytoma have been described in Syrian hamsters, which may indicate a species predilection for this unusual neoplasm.^4,5 Interestingly, all hematopoietic tumors in Syrian hamsters in 1 retrospective study were located at the ventral neck, although salivary origin was not specifically described in this study.²

Metastasis of salivary extramedullary plasmacytomas has been reported in veterinary species. One case series⁵ of two Syrian hamsters found metastasis of the extramedullary plasmacytoma to the adjacent mandibular lymph node on necropsy of one of the hamsters, while the second hamster was lost to follow-up and presence of absence of metastasis could not be confirmed. Another case report⁴ presented evidence of metastasis to a cervical lymph node in a Syrian hamster with bilateral extramedullary plasmacytomas in both mandibular salivary glands. In the sole report³ of an extramedullary plasmacytoma originating from the parotid salivary gland in a dog, metastasis to the ipsilateral medial retropharyngeal lymph node was confirmed. Unfortunately, the patient in the present report was lost to follow-up after surgical excision, and the presence or absence of metastatic disease could not be confirmed.

Salivary extramedullary plasmacytoma appears very rare in all species. However, the multiple reports of this disease process in Syrian hamsters suggest a species predilection. Furthermore, existing reports of salivary extramedullary plasmacytomas in veterinary species suggest that these tumors may have local metastatic potential, although effects on prognosis are unclear. This case alerts the clinician that salivary plasmacytoma should be a differential diagnosis for a Syrian hamster presenting with a ventral neck mass. To differentiate the diagnosis from an infection or inflammation, fine-needle aspiration for cytology is a beneficial diagnostic tool. Furthermore, evaluation of regional lymph nodes to screen for metastatic disease in these cases may be warranted.

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.