Results indicated that LAS was technically feasible in dogs and not associated with major complications. Further evaluation is required; however, in appropriately selected patients, LAS may offer the benefits of a minimally invasive technique, including a smaller incision and improved illumination and magnification during exploration and staging.

Osteosarcoma (OSA) is a malignant tumor of middle-aged dogs and adolescent humans. The clinical outcome of OSA has not improved over more than three decades, and dogs typically succumb to metastatic disease within 6 months despite tumor resection through limb amputation and adjuvant chemotherapy. Therefore, undetectable tumor cells with potential to form metastases are present at diagnosis. An assay to identify canine immortalized and primary OSA cells through flow cytometric detection of intracellular collagen 1 (Col I) and osteocalcin was optimized, and applied to blood samples from tumorbearing dogs for detection of circulating tumor cells (CTCs). Spiking variable number of OSA cells into normal dog blood recovered 50-60% of Col I positive cells with high forward and variable side light scatter. An algorithm to exclude nonviable, doublet, and autofluorescent cells was applied to sequential blood samples from three dogs obtained prior to and after limb amputation, and at approximately, triweekly intervals over 121, 142, and 183 days of chemotherapy, respectively. Dogs had >100 CTC/10 6 leukocytes prior to amputation, variably frequent CTC during chemotherapy, and an increase up to 4,000 CTC/10 6 leukocytes within 4 weeks before overt metastases or death. Sorted CTCs were morphologically similar to direct tumor aspirates and positive for Col I. Although preliminary, findings suggest that CTCs are frequent in canine OSA, more numerous than carcinoma CTC in humans, and that an increase in CTC frequency may herald clinical deterioration. This assay may enable enumeration and isolation of OSA CTC for prognostic and functional studies, respectively. OSTEOSARCOMA (OSA) is a primary bone cancer that is common in middle-aged to older, large breed dogs, and less common in humans, where children and young adults are most often affected. Therapy consisting of limb amputation or limbsparing tumor resection followed by chemotherapy (typically platinum or doxorubicin-based) is the gold standard, but the clinical outcome of OSA in dogs and humans remains poor (1-3). Dogs with OSA of the appendicular skeleton treated with amputation and chemotherapy had median survival times (STs) of 235-540 days (4), while in humans 5-year survival has been stagnant at about 60% (5). Although the median ST is relatively homogeneous, the range of ST in dogs with OSA treated identically varies from 2 to >30 months, illustrating that there is extensive heterogeneity in tumor biology and/or host response (6-8). Metastatic disease is the usual cause of spontaneous death or euthanasia, but fewer than 10% of dogs have radiographic evidence of metastasis at the time of diagnosis (2).Computed tomography also lacks sensitivity for identifying metastases, and histologic grading schemes for canine OSA poorly predict biological behavior (9-11).

Enumeration of circulating tumour cells (CTC) has shown promise for prognostication and guidance of therapeutic decisions in human cancers. The objective of this study was to enumerate CTC over time in dogs with naturally occurring osteosarcoma (OSA), and to determine correlation with patient outcome. Twenty‐six dogs with OSA and no evidence of metastatic disease at the time of amputation were enrolled. Dogs were assessed for lung metastases and CTC prior to and following amputation, and at each chemotherapy visit. Twenty‐one dogs completed the study. Nineteen dogs were euthanized and two were alive and free of metastases. Overall survival time ranged from 88 to 1058 days (median survival time (MST) 374 days). Increased serum alkaline phosphatase activity, advanced age, and higher body weight were significantly associated with lower MST. Dogs with OSA had a mean of 356 (0 to 4443) CTC/106 leukocytes. In 12 of 15 dogs that developed radiographic evidence of metastasis, a pre‐metastatic CTC spike was retrospectively detectable on average 36.5 (1–100 days) days prior to metastasis and was associated with significantly shorter MST (301 ± 64 vs. 626 ± 55 days; p = .0107). In a multivariable analysis, dogs with a CTC spike were 10× more likely to die compared with those without. These results suggest that a spike in CTC frequency precedes detection of metastasis in dogs with OSA and is associated with shorter survival. More frequent enumeration of CTC in a larger cohort of dogs with OSA may be warranted.