Reply to: Considerations on "impact of centralization of services on outcomes in a rare tumour: Retroperitoneal sarcomas". Issue 4 (April 2020) - Kalaiselvan, R.; Malik, A.K.; Rao, R.; Wong, K.; Ali, N.; Griffin, M.; Chandrasekar, C.R.; Fenwick, S.F.; Poston, G.J.; Malik, H.