Chondroblastic Osteosarcoma in Two Related Spiny-Tailed Monitor Lizards (Varanus acanthurus)

Two male spiny-tailed monitor lizard (Varanus acanthurus) broodmates were diagnosed with chondroblastic osteosarcomas associated with the pelvic girdle. One lizard was 6 months old and the other 5 months old at the time of diagnosis. Grossly, the tumors appeared as large, firm, multilobulated masses that were white on cut surface and firmly adhered to the underlying bone. Histologically, both tumors were characterized by proliferation of neoplastic spindloid to stellate cells that encompassed the vertebrae and invaded into the vertebral and pelvic bones. Both osteoid production and multifocal chondrous differentiation were observed within neoplastic masses. Retinoblastoma 1 was absent in neoplastic cells. Even though osseous neoplasms are rare amongst reptiles, Varanus spp. may have a genetic predilection for developing chondroblastic osteosarcoma.