Metastatic Chondrosarcoma in a Corn Snake (Pantherophis guttatus)

Chondrosarcomas are malignant tumors with cells that produce a matrix of cartilage with no osteoid (Thompson and Pool, 2002; Healey and Lane, 1986). They can arise in bone or periosteum, although the latter site is rare in animals. Chondrosarcomas are most frequently reported in dogs and are considered relatively common in sheep (Else, 2007) but are not common in other animals. Metastatic lesions are usually seen in the lungs but can be found in any tissue (Thompson and Pool, 2002).

An approximately two-year-old corn snake (Pantherophis guttatus) presented with a swelling of the mandible. The overlying skin was slightly discolored (Fig. 1). The lesion was treated with systemic and topical antibiotics for two months with no response. Unfortunately, the snake's condition deteriorated, and it was euthanized.

Grossly, when sectioned, the mass in the mandible was yellow–white and replaced normal bone and soft tissue of the jaw (Fig. 2). White, glistening masses were noted in numerous internal organs, including the heart (Fig. 3), kidney (Figs. 4 and 5), lung, pancreas, and eye.

The mass in the mandible was comprised of a sheet of amorphous basophilic material resembling typical cartilage matrix with slightly irregular lacunar spaces. Multiple cells were present in some lacunae. The tumor cells had abundant cytoplasm, vesicular or hyperchromatic nuclei, and prominent nucleoli. Mitotic figures were not seen. Within the myocardium, multiple foci of moderately undifferentiated chondrocytes and irregular lacunae were seen (Figs. 6 and 7). Scattered foci of neoplastic cartilaginous cells were noted within pulmonary parenchyma (Fig. 8). The masses in the kidney and pancreas were comprised of multiple to confluent foci of neoplastic cartilaginous cells. There was a proliferative mass present within the retina and subretinal tissues of one of the eyes (Fig. 9). It was comprised of moderately undifferentiated cartilage cells forming a diffuse irregular sheet. Multiple cells were present in some lacunae. There was variable distortion of the retina.

Primary chondrosarcomas are considered to arise de novo (Mankin et al., 1980), with secondary chondrosarcomas arising from preexisting cartilage. Based on this classification, the tumor in this snake was considered to be a secondary chondrosarcoma, with the primary site being the mandible. In human medicine, chondrosarcomas are classified into 3 histologic grades: I (high cellularity, plump nuclei), II (increased cellularity, distinct nucleoli, foci of myxoid change), and III (prominent nuclear atypia, mitosis), with the higher grade being positively correlated with the potential to metastasize (Lakshmanan, 2011). Using this classification scheme, the authors considered this tumor to be an intergrade between I and II, realizing that the histologic appearance and biologic behavior of the tumor in snakes may not have a direct correlation.

In a review of reptile tumors, one chondrosarcoma, site not provided, was listed in a corn snake (Maudlin and Done, 2006). Vertebral chondrosarcomas have also been described in corn snakes (Dawe et al., 1980; Garner et al., 1995), and in one case, visceral metastasis was noted (Dawe et al., 1980). A vertebral chondrosarcoma metastasizing to the liver has also been reported in a rat snake (Elaphe [Pantherophis] obsoleta obsoleta) (Honour et al., 1993), a close relative of the corn snake. Other tumors with a chondroid component have been reported in a variety of reptiles (Maudlin and Done, 2006), but only seven tumors total were listed. An osteoid chondrosarcoma has also been reported in a desert monitor (Varanus griseus) (Schönbauer et al., 1982).

Chondroid tumors are infrequent in reptiles, with corn snakes seeming to have a higher prevalence based on the literature. Grossly, these tumors must be differentiated from other forms of neoplasia and when metastatic from disseminated abscessation/bacterial infection (Page-Karjian et al., 2012).

Differential diagnoses, in addition to chronic infection, should include chondroma, chordoma (depending on location), fibrosarcoma, osteosarcoma, and metastatic tumors of any type. Chondrosarcomas are usually readily diagnosed with routine hematoxylin and eosin staining, and immunohistochemical staining is not routinely indicated. S-100 and vimentin are usually positive in low and intermediate grade sarcomas but can be focally negative in high-grade tumors (Lakshmanan, 2011).