Cancer is a complex and heterogeneous disease, influenced by various factors that affect its progression and response to treatment. Although histopathological diagnosis is crucial for identifying and classifying cancer, it may not accurately predict the disease's development and evolution in all cases. To address this limitation, liquid biopsy has emerged as a valuable tool, enabling a more precise and non-invasive analysis of cancer. Liquid biopsy offers the ability to detect tumor DNA fragments, circulating tumor cells, and exosomes released by cancer cells into the bloodstream. Exosomes, in particular, have attracted significant attention in cancer research due to their specific protein composition, which can provide valuable insights into the disease. The protein profile of exosomes often differs from that of normal cells, reflecting the unique molecular characteristics of cancer. Analyzing these proteins can help identify cancer-associated markers that play critical roles in tumor progression, invasion, and metastasis. Ongoing research and clinical validation are essential to advance and effectively utilize protein biomarkers in cancer. Nevertheless, their potential to improve diagnosis and treatment is highly promising. This review discuss several exosome proteins of interest in breast cancer, particularly focusing on studies conducted in mammary tissue and cell lines in humans and experimental animals. Unfortunately, the studies conducted in the canine species are scarce. This emphasis sheds light on the limited research available in this field. Additionally, we present a curated selection of studies that have explored exosomal proteins as potential biomarkers, aiming to achieve the aforementioned benefits in breast cancer diagnosis, prognosis, monitoring, and treatment.

Canine mammary tumors (CMTs) are among the most common disease in female dogs and share similarities with human breast cancer, which have placed these animals as a model of study in comparative oncology. Metabolic reprogramming is one of them and is known as a hallmark of carcinogenesis whereby cells undergo adjustments to supply the high bioenergetic and biosynthetic demands of rapidly proliferating cells. However, such alterations are also vulnerabilities that may serve as therapeutic strategies which have been tested mostly in human clinical trials, but poorly explored in CMTs. In this dedicated review, we compilated the metabolic changes described for CMTs emphasizing the metabolism of carbohydrates, amino acids, lipids, and mitochondrial function. We observed here key factors associated with the presence and aggressiveness of CMTs, such as the increase in glucose uptake followed by enhanced anaerobic glycolysis via upregulation of glycolytic enzymes, changes in glutamine catabolism due to overexpression of glutaminases, raise in fatty acid oxidation and distinct effects depending on the lipid saturation, in addition to mitochondrial DNA which is a hotspot for mutations. Therefore, more attention should be paid to this topic given that targeting metabolic fragilities could improve the outcome of CMTs.