In this interview, Sergio Quezada, PhD, from University College London, London, UK, discusses the presence of regulatory T (Treg) cells in the tumor environment that lead to the metastatic invasion of melanoma cells. Speaking at the 2018 National Cancer Research Institute (NCRI) Cancer Conference, held in Glasgow, UK, Dr Quezada also introduces the TRACERx study, which aims to uncover the mechanisms of the evolution of non-small cell lung cancer (NSCLC).