How reliable are circulating microRNA assays for early cancer detection in dogs, and which panels are available?

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Circulating microRNA (miRNA) assays for canine cancer detection are research-stage tools with promising diagnostic accuracy for specific tumor types, but no validated commercial miRNA panel is currently available for clinical use in dogs. The commercially available blood-based cancer screening test in dogs (OncoK9/PetDx) uses cell-free DNA (cfDNA) analyzed by next-generation sequencing to identify cancer-associated genomic alterations — it is not a miRNA assay.5 For mammary carcinoma, serum miR-19b and miR-125a are the best-characterized candidate biomarkers. Both are significantly elevated in dogs with histologically confirmed mammary carcinoma compared to healthy controls, with receiver operating characteristic area under the curve (AUC) of 0.930 for miR-125a and 0.880 for miR-19b.1 Serum miR-18a is elevated specifically in mammary carcinoma dogs with histologic evidence of lymphatic invasion, giving it potential prognostic rather than purely diagnostic utility.1 No miRNA showed significant association with survival in that cohort.1 For splenic hemangiosarcoma, a four-miRNA panel — miR-126-5p, miR-150-5p, miR-452-5p, and miR-543 — discriminates hemangiosarcoma from noncancerous splenic masses, with miR-543 upregulated 8.9-fold in hemangiosarcoma dogs.2 Whether this panel performs equivalently for hemangiosarcoma in non-splenic locations has not been established.2 For gastrointestinal cancer versus chronic inflammatory enteropathy, fecal and serum miRNA panels show the strongest diagnostic performance reported across any canine cancer miRNA work to date. Fecal miR-451 achieves AUC 0.955 (sensitivity 86.4%, specificity 100%), fecal miR-223 achieves AUC 0.918 (sensitivity 90.9%, specificity 80%), and fecal miR-27a achieves AUC 0.868 (sensitivity 81.8%, specificity 90%) for distinguishing gastrointestinal cancer from chronic inflammatory enteropathy.3 On the serum side, miR-652 achieves AUC 0.943 (sensitivity 90.5%, specificity 90%), miR-148a-3p achieves AUC 0.924 (se