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Tumors of Bone and Joint

1
1
Stephanie L. Shaver, DVM, DACVS , William T.N. Culp, VMD, DACVS , and
Robert B. Rebhun, DVM, PhD, DACVIM (Oncology) 2
1 School of Veterinary Medicine, University of California, Davis, Davis, CA, USA
2 Department of Surgical and Radiological Sciences, University of California, Davis, Davis, CA, USA

Etiology/Pathophysiology often metastasize to other bony sites; however, metastatic
bony lesions secondary to other cancers are also com-
Primary tumors of bone are most commonly diagnosed mon. Many carcinomas, particularly those arising from
in the appendicular skeleton, with osteosarcoma (OSA) the urogenital tract, often demonstrate a propensity for
being the most common tumor type. Other neoplasms, bony metastasis. While not absolute, metastases are
such as chondrosarcoma (CSA), fibrosarcoma (FSA), commonly found in the diaphysis, whereas primary bone
hemangiosarcoma (HSA), and histiocytic sarcoma, are tumors generally occupy the metaphyseal region.
less frequently identified. The metaphyseal region of Axial skeletal neoplasia may be caused by any of the
long bones is the typical location for appendicular OSA, sarcoma types that affect the appendicular skeleton.
with the distal radius and proximal humerus being the OSA remains the most common tumor in axial locations
two most common sites. The proximal tibia and distal as well, although it only accounts for about 25% of all
femur may also be affected, with proximal femur, distal cases of axial skeletal neoplasia. The mandible and max-
tibia, distal humerus, and ulna being less common sites. illa are the sites most often affected, but other bones of
While many possible contributing factors have been the skull, the scapula, ribs, sternum, vertebrae, and pelvis
suggested, the precise etiology of OSA remains unknown. may also be affected. Multilobular osteochondrosarcoma
Suspected risk factors include previous radiation ther- (MLO, also known as multilobular tumor of bone) typi-
apy, fracture, and metal surgical implants. There is also cally affects the flat bones of the skull and is a slow‐grow-
some evidence that the timing of spay/neuter may affect ing, locally invasive tumor. The metastatic propensity of
the incidence of OSA, but a clear causal effect has not MLO is largely dependent upon grade. In general, mor-
been demonstrated. tality from axial skeletal neoplasia occurs from local dis-
Osteosarcoma is characterized by proliferation of ease rather than metastasis, likely due to the challenging
endosteal cells, which results in the tumor arising within nature of surgical resection in these areas. Mandibular
the medullary canal. This is responsible for the typical OSA appears to have a better prognosis than OSA in
radiographic appearance of bony lysis and periosteal appendicular or other axial locations. Improved progno-
reaction. Two less common OSA variants, periosteal and sis may result from less aggressive biologic behavior
parosteal, exist. Periosteal OSA arises from cortical bone when compared with appendicular sites and from the
but may invade the medullary canal; in contrast, parosteal relative ease of complete surgical excision compared
OSA is characterized by the development of tumor with other axial sites.
external to the cortex, which does not invade into deeper Synovial cell sarcoma has been reported to be the most
structures. While extremely rare, parosteal OSA likely common canine joint tumor; however, other reports also
represents a less aggressive form of OSA. describe a high incidence of histiocytic sarcoma affect-
Other neoplastic processes that can affect bone include ing synovial surfaces. These tumors most commonly
hematopoietic tumors (such as lymphoma, histiocytic affect large joints of the appendicular skeleton (e.g., sti-
sarcoma, or multiple myeloma) and metastasis from a fle, elbow), and have biologic behavior similar to these
solid tumor. Primary bone tumors such as osteosarcoma tumor types in other locations. Suspicion of a joint tumor

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical