ABSTRACT

Background and Aim: Canine mammary gland tumors (CMTs) are among the most important neoplasms in female dogs and provide a valuable spontaneous model for comparative oncology. Despite advances in surgery and chemotherapy, treatment of advanced and metastatic CMTs remains limited by therapeutic resistance, systemic toxicity, and poor clinical outcomes. Phytochemicals and standardized botanical extracts have therefore attracted interest as multitarget anticancer agents and potential chemosensitizers. This review critically evaluates their molecular mechanisms, therapeutic synergy, safety, and translational potential in CMTs. Peer-reviewed literature published from January 2014 to August 2026 was identified through PubMed, Web of Science, and Google Scholar using a systematic search framework. Of 342 records identified, 254 unique records were screened, 36 full-text articles were assessed, and 10 primary experimental studies met the inclusion criteria. These studies evaluated six single-molecule phytochemicals and four standardized botanical extracts across CMT cell lines and preclinical in vivo models. Caspase-dependent apoptosis and modulation of the mitochondrial Bcl-2/Bax axis were the most consistently demonstrated anticancer mechanisms, while phase-specific cell cycle arrest, autophagic flux modulation, and suppression of oncogenic signaling provided additional therapeutic targets. Celastrol showed the greatest in vitro potency, with a half-maximal inhibitory concentration (IC₅₀) below 1.3 μM, whereas esculetin required substantially higher concentrations and had a narrower safety margin. Combination strategies were particularly promising; curcumin with cyclophosphamide produced strong synergistic effects and enabled substantial cytotoxic dose reduction, while resveratrol combined with Viscum album extract demonstrated complementary anticancer activity. Conversely, indole-3-carbinol reduced primary tumor proliferation but paradoxically increased tumor embolization and visceral metastasis in vivo, emphasizing the need for rigorous safety assessment. Clinical translation remains constrained by poor oral bioavailability, rapid metabolism, inadequate canine-specific pharmacokinetic (PK) data, formulation variability, and the absence of prospective trials in dogs with spontaneous CMTs. Future research should prioritize standardized formulations, advanced drug delivery systems, canine PK and safety studies, and biomarker-driven clinical trials to determine whether promising phytochemicals can be translated into safe, effective adjunctive therapies for canine mammary oncology.

Keywords: anticancer phytochemicals, apoptosis, botanical extracts, canine mammary gland tumors, comparative oncology, pharmacokinetics, therapeutic synergy, translational oncology.