Abstract
Circulating tumor cells (CTCs) are precursors of metastasis in various cancer types. Many aspects regarding CTC biology remain poorly understood. Here, we describe mass spectrometric analysis of CTCs from a breast cancer xenograft mouse model, including procedures comprising CTC enrichment, separation of different CTC subpopulations, and their quantitative proteomic assessment. This protocol aims to facilitate the identification of protein content dynamics in human CTCs that are physiologically shed from tumor-bearing xenografts, providing a framework for investigating metastasis biology. For complete details on the use and execution of this protocol, please refer to Donato et al. (2020).