Introduction

Neoplasia is considered uncommon in degus, with previous research indicating a low incidence in this species. A study by Jekl et al. (2011) found that only six out of 300 pet degus examined showed evidence of neoplastic disease. Among the reported cases, fibrosarcomas have been identified as the most prevalent cutaneous neoplasm, as highlighted in a study by Svara et al. (2020). This study aims to retrospectively analyse cutaneous neoplasms in pet degus within the United Kingdom, providing further insight into their occurrence and characteristics.

Results

A systematic review of archived case material identified 35 skin neoplasms in pet degus, with 31 of these diagnosed as sarcomas, making them the most prevalent tumour type in this species. The average age at diagnosis was five years, with cases ranging from two to nine years old. Among the affected degus, 16 were male, 11 were female, and for four cases, age details were not recorded on the submission form. Sarcomas most commonly occurred on the rump or legs, with fewer cases involving the head or neck. Histopathological examination revealed a range of sarcoma types, from well-differentiated spindle cell sarcomas to pleomorphic sarcomas exhibiting multinucleated cells.

Figure 1: Age distribution of the patients.

Figure 2: Sites of cutaneous sarcomas.

 

Immunohistochemistry confirmed vimentin expression, supporting a mesenchymal origin. Further analysis of selected cases for the histiocytic marker Iba-1 and the muscle marker desmin showed that all tested samples were negative for Iba-1, while some exhibited desmin expression in a subset of neoplastic cells. Regarding surgical excision, 22 tumours were submitted as excisional samples, but only six cases achieved complete excision. Additionally, four sarcomas were submitted following limb amputation, with three showing no evidence of residual tumour tissue.

 

Discussion

This study confirms that the majority of cutaneous neoplasms in pet degus are sarcomas, reinforcing previous findings on neoplastic trends in this species. Interestingly, the results indicate that these tumours were more commonly found in male degus, which contrasts with earlier research by Svara et al. (2020), where cutaneous sarcomas were reported as more prevalent in females. This discrepancy highlights the need for further investigation into potential sex-related predispositions or underlying factors influencing tumour development.

 

Figure 3: Histopathological features of cutaneous sarcomas in degus.
Left: well-differentiated sarcoma forming streams and exhibiting low mitotic activity.
Right: Poorly-differentiated sarcoma exhibiting multinucleated cells (asterisk) and frequent mitotic figures (arrows). H&Estain. Scale bar = 100μm

 

Histological and immunohistochemical analysis confirmed that these neoplasms were consistent with soft tissue sarcomas. The expression of desmin in some cases suggests a possible smooth muscle, skeletal muscle, or myofibroblast origin. Additionally, the absence of Iba-1 expression indicates that none of the tumours represented histiocytic sarcomas. Notably, no cases of cutaneous hemangiosarcomas or extra-osseous osteosarcomas were identified within this study population. Despite attempts at complete surgical excision in 26 out of 31 cases, histological examination confirmed that only nine achieved lesion-free tissue borders, emphasising the challenges of achieving clear surgical margins in these tumours.

 

Figure 4: Immunohistochemistry analysis.
Left: Neoplastic cells exhibit expression of vimentin.
Right: Occasional neoplastic cells exhibit expression of desmin. Scale bar = 100μm

 

Materials and methods

Study population

A systematic review of archive material of skin masses from degus submitted for histopathological evaluation to the authors’ laboratories between 2012 and 2024 was carried out. The age, sex , site and surgical procedure (excisional or incisional biopsy) were analysed based on the information given on the submission form.

Histopathology and immunohistochemistry analysis

For a review of all sarcoma cases the formalin-fixed paraffin-embedded tissue samples were sectioned at a thickness of 2-3 μm and stained with haematoxylin and eosin (H&E). For immunohistochemistry analysis antigen retrieval, labelling and counterstaining were performed on an Autostainer Link 48 (Agilent, Stockport, UK) using the En Vision Flex detection system (Agilent).

Primary antibody dilutions were 1:1000 for vimentin (Agilent), 1:800 for Iba-1 (EMD Millipore, Darmstadt, Germany) and 1:200 for desmin (Agilent) Target retrieval for all three antibodies was performed using Target retrieval solution high pH (Agilent). Sections were counterstained using haematoxylin.

Conclusions

Soft tissue sarcomas were the most common skin masses identified in degus in this study. On histological examination excision was often incomplete; however follow-up studies are required to determine the clinical outcome and prognosis of these tumours.

References

JEKL, V., HAUPTMAN, K. & KNOTEK, Z. (2011) Diseases in pet degus: a retrospective study in 300 animals. Journal of small animal practice 52 (2), 107-12 .

ŠVARA T., GOMBAČ M., POLI A., RAČNIK J. & ZADRAVEC M. (2020). Spontaneous Tumors and Non-Neoplastic Proliferative Lesions in Pet Degus (Octodon degus). Veterinary Sciences.13;7(1):32.