Galardi F, De Luca F, Biagioni C, et al. - Researchers focused on the prognostic role of circulating tumor cell (CTC) counts among patients included in the cTREnd study (a pre-planned translational sub-study of TREnd) that randomly assigned patients suffering from advanced breast cancer (ABC) to palbociclib monotherapy or palbociclib plus the endocrine therapy received in the previous line of treatment. They also assessed RB1 (retinoblastoma 1) gene expression on CTCs as well as investigated its prognostic role within the cTREnd subgroup. They studied 46 pstients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative ABC. Based on findings, CTC count appeared as a promising tool to monitor palbociclib response. Clinical results after palbociclib could be predicted by CTC count at the time of progression. Not only the feasibility of RB1 expression analysis on CTCs was evident but also it may offer additional prognostic information.