Table 1.

Summary of the literature review based on the analysis of tumour-derived material from HR+/HER2- advanced breast cancer patients using liquid biopsy. (NGS: Next Generation Sequencing, ddPCR: droplet-digital PCR, qPCR: quantitative PCR)

Tumour-Derived Material	Biomarker	Therapy	Technique	References
ctDNA	RB mutations	PALOMA 3: Palbociclib plus fulvestrant	Exome sequencing NGS ddPCR	O’Leary B, Cutts RJ, Liu Y, et al. [3]
		Palbociclib plus fulvestrant Ribociclib plus letrozole	NGS	Condorelli R, Spring L, O’Shaughnessy J, et al. [49]
	ESR1 mutations	PALOMA 3: Palbociclib plus fulvestrant	Exome sequencing NGS ddPCR	O’Leary B, Cutts RJ, Liu Y, et al. [3]
			ddPCR	Fribbens C, O’Leary B, Kilburn L, et al. [50]. O’Leary B, Hrebien S, Morden JP, et al. [51]
		Palbociclib plus AI/fulvestrant	Exome sequencing NGS	Wander SA, Cohen O, Gong X, et al. [35]
	FGFR1 mutations	MONALEESA-2: Ribociclib plus letrozole	NGS qPCR	Formisano L, Lu Y, Servetto A, et al. [52]
			NGS	Hortobagyi GN, Stemmer SM, Burris HA, et al. [53] Neven P, Petrakova K, Bianchi GV, et al. [54]
	PI3K mutations	PALOMA 3: Palbociclib plus fulvestrant	Exome sequencing NGS ddPCR	O’Leary B, Cutts RJ, Liu Y, et al. [3]
			BEAMing assay ddPCR	Cristofanilli M, Turner NC, Bondarenko I, et al. [48] O’Leary B, Hrebien S, Morden JP, et al. [51]
CTC	CTC enumeration RB1 expression	TREnd trial: Palbociclib monotherapy Palbociclib plus ET	CellSearch System ddPCR	Galardi F, De Luca F, Biagioni C, et al. [55]
EVs	CDK9/4 and TK1 mRNA copies	ECLIPS study: CDKi plus endoncrine theraphy	ddPCR	Del Re M, Bertolini I, Crucitta S, et al. [56]
	miRNA 432-5-p	Palbociclib plus letrozole/fulvestrant	mRNA/miRNA array NGS	Cornell L, Wander SA, Visal T, Wagle N, Shapiro GI [57]