Spontaneous soft tissue tumours in aged mouse lemurs (Microcebus spp)

Mouse lemurs (Microcebus spp) are small Madagascan strepsirrhine primates increasingly used as an animal model in ageing research. During a period of 10 years, neoplastic disease occurred in 47 grey (Microcebus murinus) and Goodman's (Microcebus lehilahtsara) mouse lemurs from a captive colony in Germany. Approximately half of these tumours appeared histologically as soft tissue tumours (STTs) with a significantly higher proportion of STTs in Goodman's mouse lemurs (87.5%) compared with grey mouse lemurs (38.5%) (P ≤0.025). Most STTs grew subcutaneously in old or senile animals and were commonly located on the trunk, less often on the head and rarely at visceral sites. The majority of STTs were of fibrous or myofibroblastic origin, followed by undifferentiated pleomorphic sarcomas and extraskeletal chondro-osseous neoplasia. Histological grading of malignant STTs revealed all but one as grade II or III, with more than 60% being grade III. Female mouse lemurs of both species were affected significantly more often by grade II and III tumours than males (P = 0.0412). This study gives a comprehensive overview of the spectrum of mesenchymal neoplastic disease in mouse lemurs and highlights some histomorphological characteristics of spontaneous STTs in this small non-human primate species.