Despite this, recent data has suggested that the majority of canine cancers are Luminal A or Luminal B in phenotype (ER+/− or PR+/− but not both deleted and erbB-2/HER-2− for Luminal A and erbB-2/HER-2+ for Luminal B) with the most aggressive forms often being characterized as HER-2 positive (ER−, PR−, erbB-2/HER-2+) in canine patients [14,43]. This evidence concerns the gene PGR and cancer.