MARSUPIALS - GENERAL

Most marsupial groups are moderately or markedly sus­ceptible to neoplasia. A review of the literature (1900- 2018) and the ARWH database (1998-2018) (ARWH 2018) identified 579 cases of neoplasia in marsupials.

1.1 Cutaneous and subcutaneous tumours in marsupials

A total of 82 cutaneous neoplasms were identified, of which 41 (50%) were benign, 2 (2.4%) were pre-malig- nant, and 39 (47.6%) were malignant. Squamous cell car­cinoma (SCC) was the most common cutaneous neoplasm (20%). It is considered a locally invasive tumour with a slow rate of metastatic spread in domestic species; however, 20% of SCC in marsupials had metasta­sised by the time of necropsy, suggesting an increased propensity to or rate of metastasis in marsupials (Beck et al. 2017; ARWH 2018). Cutaneous lymphosarcoma rep­resented 10% of the total number of cutaneous neoplasms in marsupials.

Subcutaneous tumours are less frequent, though tended to have a poorer prognosis. Feather-tailed gliders (Acrobates spp.) are predisposed to SC transponder-asso­ciated sarcomas (see section 5.1).

Specific cutaneous and SC neoplasms documented in marsupial species are listed in the relevant taxonomic sections of this chapter.

Table 18.1. Important species-specific neoplastic diseases in Australian mammals

1.1.1 Diagnosis

Principles of diagnosis used in domestic animals can be followed, typically utilising cytology and/or incisional or excisional biopsy.

1.1.2 Treatment

Cutaneous tumours in marsupials are anecdotally amena­ble to surgical resection. Principles of surgical excision used for domestic animals are appropriate. In four of five marsu­pials that had benign skin tumours surgically excised there was no reported recurrence, including a red-tailed phas- cogale (Phascogale calura) with apocrine adenoma (ARWH 2018 case no. 11903.1), two Tasmanian devils (Sarcophilus

Fig. 18.1. Long-nosed bandicoot (Perameles nasuta): thorax, lateral view. The animal had a large clinically detectable soft tissue mass (sarcoma) in the caudal abdomen. Radiographs of the thorax revealed a mixed pattern of increased pulmonary opacity, histologically identified as metastatic sarcoma throughout the lung.

harrisii) with epithelioma (ARWH 2018 case nos 8321.1,

8852.1) and a southern hairy-nosed wombat (Lasiorhinus Iatifrons) with a tricholemmoma (ARWH 2018 case no.

12127.1). A long-nosed bandicoot (Perameles nasuta) had a sebaceous adenoma excised from the right shoulder, though 10 mo later an aggressive mass developed at the same site and was diagnosed at necropsy as a soft-tissue sarcoma (STS) (ARWH 2018 case no. 6855.1). Surgical excision was curative in two cases of SCC-in-situ, in a Tasmanian devil and a swamp wallaby (Wallabia bicolor) respectively (ARWH 2018 case nos 8321.3, 9897.2).

Four malignant cutaneous tumours were surgically treated, three successfully (specifically, a basal cell carci­noma and a malignant perioral trichoepithelioma in two greater bilbies (Macrotis lagotis) [ARWH 2018 case nos 3112.1, 8167.1] and a SCC in a koala [ARWH 2018 case no. 3089.2]). A SCC was excised from a Tasmanian devil, but it was euthanased 4 mo later with metastatic SCC (ARWH 2018 case no.

Subcutaneous tumours have a poorer rate of surgical treatment success than cutaneous tumours. Of four cases treated surgically, including two lipomas and two STS, treatment was only successful in one case of lipoma in a red kangaroo (Osphranter rufus) (ARWH 2018 case no.

8082.1). A yellow-bellied glider (Petaurus australis) had a patagial lipoma excised, though 2 yr later at necropsy it had generalised lipomatosis and a transponder-associated infiltrative lipoma (ARWH 2018 case no. 7086.1). Surgical excision of digital STS in an eastern barred bandicoot (P. gunnii) (ARWH 2018 case no. 2965.2), and SC STS in a feather-tailed glider (ARWH 2018 case no. 8630.2) was unsuccessful in both cases. The bandicoot also had inva­sive sarcoma more proximally in the affected limb and was euthanased 10 d later. The glider died after 11 d in care and was diagnosed with multicentric lymphosarcoma at necropsy, though with no evidence of spread of the STS.

Only one report of attempted non-surgical treatment was identified, in a Tasmanian devil with cutaneous lymphosarcoma. Chemotherapy was attempted with Iomustine, which did not slow progression of the lympho­sarcoma and the animal was euthanased within 2 mo (Scheelings et al. 2014).

1.2 Mammary tumours in marsupials

Most mammary tumours documented in marsupials are malignant. Of the 10 diagnostic and necropsy cases of mammary neoplasia in the ARWH (2008-17), 20% were benign, 20% were pre-malignant (carcinoma-in-situ) and 60% were malignant (carcinoma or adenocarcinoma) by the time of biopsy or death (ARWH 2018 case nos 8707.1, 8777.2, 8777.3, 8850.1, 10231.1, 11127.1, 11279.2, 11637.1, 11792.1, 12162.1). A case series of 15 mammary neoplasms diagnosed at biopsy or necropsy from macropods living in the USA found that 90.7% were malignant (carcinoma) (Hsu et al. 2022). Application of canine mammary carci­noma classification and grading protocols (Goldschmidt et al. 2011; Pena et al. 2013) to these macropod mammary carcinomas showed promise for prognostic prediction, with Grade 3 carcinomas and comedocarcinomas in macropods being linked to a higher rate of metastatic spread (Hsu et al.

1.2.1 Diagnosis

Principles of diagnosis as per domestic animals can be used and assessment should include local and distant lymph node palpation (± cytology) and radiographs of the abdomen and thorax to exclude metastasis. Cytologi­cal examination of aspirates from masses can be per­formed, but caution should be exercised as hyperplastic, benign, and malignant mammary tumours are often dif­ficult to differentiate using cytology alone. If the animal is a suitable candidate for surgery, then incisional or exci­sional biopsy is recommended.

1.2.2 Treatment

Mammary tumours in marsupials may be amenable to surgical resection, particularly if diagnosed early. Exci­sion with wide margins, or partial or total pouch ablation, is an option for more extensive, recurrent or bilateral tumours (see Chapter 10). In four of six cases with treat­ment and outcomes recorded there was a successful out­come. Surgical management was the only form of treatment attempted in all cases. Both excisional biopsy and pouch ablation were used, the latter in cases of bilat­eral tumours or recurrent masses. Descriptions of case outcomes are provided in Table 18.2.

2.