ESR1 and cancer: Beyond the polyphenol metabolism, bioavailability, and time of exposure, several factors related to their (anti) estrogenicity on ERα and/or ERβ define the complexity of polyphenols’ effects on cancer cells and sustain the need for a deep understanding of the molecular pathways involved in the ER-mediated effects of polyphenols on the cancer initiation, progression, and development that impact on the overall disease process.