Depends on the type of the biomarker, at first you need to know which biomarkers you are looking for? means which biomarkers are most probably expressed in saliva during breast cancer, as different biomarkers have different expression rate. TQ

Sialic acid belonging to a family of monosaccharides, an important component of glycoproteins, linked to the end of the glucan chain. In relation to breast cancer and sialic acid, an increase in serum concentration has already been determined in this pathology and its possible relationship with the stage of the disease. In Mexico there is a line of research about the determination of the salivary concentration of sialic acid. Arteaga et al. They performed a study of salivary sialic acid in breast cancer, where the concentration was determined by means of spectroscopy and found an increase in the salivary concentration of sialic acid in patients with breast cancer compared to healthy patients.

these two web address answers your questions

https://www.croh-online.com/article/S1040-8428(16)30388-2/fulltext

https://www.nature.com/articles/ijos201638