In dogs with primary liver tumors, additional liver masses identified on preoperative imaging or surgical exploration are most often benign.

Abstract

OBJECTIVE: To evaluate the malignancy status of additional masses in dogs with a primary liver mass. The hypothesis was that the malignancy status of the primary liver mass would not be related to the malignancy status of the biopsied additional mass. METHODS: This retrospective study evaluated canines receiving a liver lobectomy for a primary liver tumor with concurrent biopsy of an additional liver mass and subsequent histopathologic diagnoses from January 1, 2019, to May 15, 2025, at a single institution. RESULTS: 40 dogs were identified. All 22 benign primary masses had benign additional masses. Sixteen malignant primary masses had benign additional masses, and 2 malignant primary masses had malignant additional masses. The second mass was benign in 38 of 40 dogs (95%). CONCLUSIONS: In dogs with multiple liver masses, a malignant primary liver mass did not correlate with a malignant secondary mass. Dogs with a primary liver mass that was excised were not found to have a significant incidence of the additional mass representing metastasis. CLINICAL RELEVANCE: Benign additional liver masses frequently occur in dogs with primary liver masses. Additional masses should not be overinterpreted as a strong indicator of metastatic disease when discussing the results of staging diagnostics with clients, as most dogs have an excellent prognosis with liver lobectomy.