Predictors of histologically confirmed local recurrence and no evident association of wound soaker catheter use with local recurrence in dogs with grade II–III mammary carcinomas: a retrospective cohort study

Introduction Local recurrence after mammary surgery is a clinically relevant outcome in dogs with mammary carcinomas, yet recurrence-specific prognostic factors and the oncologic safety of wound soaker catheters (WSCs) remain insufficiently defined. Methods This retrospective cohort study aimed (1) to identify clinicopathologic factors associated with time to histologically confirmed local recurrence in dogs with grade II–III mammary carcinomas and (2) to evaluate whether WSCs delivering intermittent bupivacaine boluses were associated with the hazard of local recurrence. Standardized records from a veterinary teaching hospital were reviewed for female dogs undergoing nodulectomy, regional mastectomy, or unilateral radical mastectomy with histologic confirmation of grade II–III carcinoma. Local recurrence was strictly defined as histologic regrowth at or near the surgical site, and time to local recurrence was analyzed using Cox proportional hazards models. Results The cohort included 117 dogs (65.0% grade II; 35.0% grade III), of which 11 (9.4%) developed local recurrence, with a median time to recurrence of 6.4 months. In the multivariable model based on 107 complete cases, larger tumor size (hazard ratio [HR] 1.29 per 1-cm increase; 95% confidence interval [CI] 1.07-1.55) and histologic infiltration (HR 4.51; 95% CI 1.43-14.23) were independently associated with a higher hazard of local recurrence. WSC use was not associated with the hazard of local recurrence (HR 0.36; 95% CI 0.09–1.40), although the estimate was imprecise. Discussion Overall, these findings suggest that tumor size and histologic infiltration are associated with histologically confirmed local recurrence, and they do not provide evidence that WSC-based local analgesia increases the hazard of local recurrence within the limitations of this retrospective cohort.