Although the upregulation of miR-18a and miR-18b has been previously demonstrated in canine mammary carcinomas [31,32], to the best of the authors’ knowledge, no study has previously explored the correlation between these miRNAs and their main target mRNA (i.e., ESR1 mRNA), as well as the correlation between miR-18 and miR-18b expression, ERα immunoexpression and Ki67 index in CMTs. Here, MKI67 is linked to breast carcinoma.