Apocrine gland anal sac adenocarcinoma (AGASACA) is locally aggressive and highly metastatic to regional lymph nodes. The aim of this study was to evaluate the prognostic significance of Ki67 in surgically excised AGASACA. Prognostic impact of size, regional lymph nodes metastasis, hypercalcemia, histologic pattern, mitotic count, necrosis, inflammatory and lympho-vascular invasion, anisokaryosis and anisocytosis was also evaluated. Thirty-five dogs were included, twenty-four of which also had metastatic lymph nodes. When the entire population was evaluated, only metastatic disease spread to regional lymph nodes, and necrosis and inflammatory infiltration were correlated to prognosis. When only dogs with metastatic disease were evaluated, size, solid histologic pattern, presence of lymphatic and vascular invasion showed influence on prognosis. Ki67 index was not associated with survival time and disease free interval in any case. The results of this study showed that lymph nodes metastasis at diagnosis reduced disease free interval. Moreover, tumor size greater than 5.25 cm, presence of lymphatic and vascular invasion and a solid histologic pattern were associated with a shorter survival time in dogs with metastasis to regional lymph nodes. Ki67 expression was not significantly associated with prognosis, therefore it could not be considered as a prognostic factor in this tumor type, while the role of hypercalcemia remained unclear.

Canine apocrine gland anal sac adenocarcinoma (AGASACA) is an aggressive canine tumor originating from the anal sac glands. Surgical resection, with or without adjuvant chemotherapy, represents the standard of care for this tumor, but the outcome is generally poor, particularly for tumors diagnosed at an advanced stage. For this reason, novel treatment options are warranted, and a few recent reports have suggested the activation of the immune checkpoint axis in canine AGASACA. In our study, we developed canine-specific monoclonal antibodies targeting PD-1 and PD-L1. A total of 41 AGASACAs with complete clinical and follow-up information were then analyzed by immunohistochemistry for the expression of the two checkpoint molecules (PD-L1 and PD-1) and the presence of tumor-infiltrating lymphocytes (CD3 and CD20), which were evaluated within the tumor bulk (intratumor) and in the surrounding stroma (peritumor). Seventeen AGASACAs (42%) expressed PD-L1 in a range between 5% and 95%. The intratumor lymphocytes were predominantly CD3+ T-cells and were positively correlated with the number of PD-1+ intratumor lymphocytes (ρ = 0.36; p = 0.02). The peritumor lymphocytes were a mixture of CD3+ and CD20+ cells with variable PD-1 expression (range 0–50%). PD-L1 expression negatively affected survival only in the subgroup of dogs treated with surgery alone (n = 14; 576 vs. 235 days). The presence of a heterogeneous lymphocytic infiltrate and the expression of PD-1 and PD-L1 molecules support the relevance of the immune microenvironment in canine AGASACAs and the potential value of immune checkpoints as promising therapeutic targets.

Several studies evaluating Ki67 in canine cutaneous mast cell tumors (cMCTs) have reported its prognostic value when tumors of all histological grades are included. This study aims to evaluate whether the Ki67 index has a predictive value in a homogeneous cohort of G2/LG cMCTs with HN2 lymph nodes (LNs) and to describe the clinical outcome. The second goal was to explore the correlation between the Ki67 index and MC. The medical databases of three institutions were retrospectively searched for dogs undergoing surgical treatment for cMCT and LN extirpation, with a histological diagnosis of G2/LG with HN2 LNs. Information about histological margins, MC, Ki67 index, local recurrence, nodal relapse, distant metastasis, de novo cMCT occurrence and date and cause of death were included. A total of 39 cases were identified. None of these developed local and nodal relapse or metastatic distant disease. Median MC was 1 (0–2). Median Ki67 index was 3.5 (0.7–14.3). Ki67 and MC were not significantly correlated. At the end of the study, 32 (82%) dogs were alive, 7 (18%) dogs were dead from unrelated causes and 4 (10.2%) dogs were lost to follow-up. The median ST was not reached, and the mean was 893 days (104–2241 days). Considering the strict inclusion criteria, dogs affected by G2/LG with HN2 LNs treated with surgery alone may have a good oncologic outcome; the Ki67 index does not have prognostic impact.