Department of Veterinary and Biomedical Sciences

Erin Burton Publishes Manuscript in AVMA Journal

October 4, 2017
Burton, Erin

The paper "Pathology in Practice," outlines a case of chondrosarcoma in a 12-year-old, male, boston terrier. 

For the dog of the present report, a diagnosis of chondrosarcoma was suspected from the cytologic findings for the fine-needle aspirate specimens, and was confirmed during histologic examination of sections of the hard palate mass. Although neither diagnostic imaging nor a necropsy was performed, the nasal cavity was suspected to be the primary site of origin on the basis of the physical examination findings.

Chondrosarcomas are most commonly detected in medium- or large-breed dogs that are 5.9 to 8.7 years of age with no sex predilection. In 1 study involving 97 dogs, Golden Retrievers were overrepresented; however, the proportions of Boxers and German Shepherd Dogs with chondrosarcomas were also high. Cats with this neoplasm have also been described. Unlike dogs, cats do not have an associated breed predisposition; however, there is a sex predilection, and males are 1.9 times as likely to develop these tumors as are females. The mean age for tumor development is approximately 9.6 years in cats.

Chondrosarcoma is a malignant neoplasm in which the cells produce variable amounts of cartilaginous and fibrillar matrix, but never produce osteoid. Like other mesenchymal neoplasms, these tumors may not exfoliate well; therefore, fine-needle aspiration may yield specimens with low numbers of individualized or loosely aggregated, plump, ovoid to spindle–shaped cells. Small to moderate numbers of eosinophilic to purple cytoplasmic granules may be present, and cytoplasmic borders are often indistinct. Occasionally, mesenchymal cells are noted to be within circular structures consistent with lacunae. Brightly eosinophilic, streaming matrix is often closely associated with these cells. These cytologic features can also be seen with other tumors such as chondromas, chondroblastic osteosarcomas, multilobular osteochondrosarcomas, or other cartilage-producing neoplasms. Lack of evidence of alkaline phosphatase activity after application of the cytochemical reagent 5-bromo-4-chloro-3′-indolyphosphate p-toluidine salt and nitro-blue tetrazolium chloride (BCIP/NBT) in cytologic specimens can be helpful in increasing the suspicion of a chondrosarcoma rather than an osteosarcoma. Nevertheless, some chondrosarcomas have cytochemically detectable alkaline phosphatase activity. It is also possible for a cytologic preparation to lack the osteoblastic component of a chondroblastic osteosarcoma or multilobular osteochondrosarcoma; therefore, caution should be used when interpreting alkaline phosphatase staining patterns. Histologic examination of sections of lesions is essential for definitive diagnosis.

Although chondromas are considered rare in dogs and cats, it can be difficult to histologically distinguish between a low-grade chondrosarcoma and a chondroma because malignant features are often subtle. Therefore, tumor behavior and results of advanced diagnostic imaging are often used in conjunction with histopathologic findings to help distinguish a low-grade chondrosarcoma from a chondroma. Histologically, a chondrosarcoma is composed of numerous disorganized lacunae containing variably pleomorphic chondrocytes. The chondrocytes are typically ovoid to spindloid and produce variable amounts of basophilic to eosinophilic chondroid matrix. In general, this neoplasm often has a low mitotic rate; however, higher mitotic indices may be evident with more aggressive forms.

Chondrosarcomas can be further classified as primary or secondary depending on the origin of the tumor. Primary chondrosarcomas originate from within bone or periosteum, whereas secondary chondrosarcomas are derived from malignant transformations of cartilage from an osteochondroma. Primary chondrosarcomas are more frequently identified and are the second most common bony neoplasm, accounting for approximately 10% of bone tumors in dogs. Sixty-one percent of these tumors are associated with flat bones. The most common sites are the ribs, nasal turbinates, and pelvis. In contrast, 63% of these tumors are associated with the long bones in cats, and the most common sites are the femurs and digits. The remainder (37%) of these tumors are associated with the flat bones, of which the scapula is most commonly affected.

Chondrosarcomas typically grow slowly and rarely metastasize. The overall median survival time can vary widely based on the location of the neoplasm. Tumors for which complete surgical excision can be achieved are usually associated with good prognoses and long median survival times. Nasal chondrosarcomas have variable median survival times, regardless of the treatment, ranging from 210 to 580 days. Owing to the anatomic location, surgical debulking procedures are difficult and associated with complications; local reoccurrence is a common sequela. These tumors also unfortunately do not respond well to radiation therapy. Therefore, in cases of nasal chondrosarcoma, despite the low metastatic potential, local recurrence and invasion of the surrounding tissue are the primary reasons for treatment failure and ultimately euthanasia.