Fig. S1 demonstrates that human CAFs survive within xenograft tumors Fig. S2 shows the results of quality control for CRISPR-mediated knockout cell lines Fig. S3 shows enhanced tumor growth is ESCC cells are co-implanted with CAF Fig. S4 shows data supporting the role of IL-6 as a mediator of tumor-stroma cross-talk Fig. S5 demonstrates that IL-6 is produced by both ESCC cells and CAFs via RNA in situ hybridization Fig. S6 shows that IL-6 and IL-6Ra are expressed by ESCC cells Fig. S7 shows that exogenous IL-6 rescues the IL-6 knockout phenotype Fig. S8 shows that tocilizumab treatment stalls growth of ESCC and EAC 3D tumoroids Fig. S9 shows the growth curves and IHC staining for pSTAT3, pERK, Ki-67 and cleaved caspase 3 for ESCC tumor xenografts treated with tocilizumab Fig. S10 demonstrates that tosilizumab treatment reduces angiogenesis (via lectin staining) Fig. S11 quantifies the histological changes in tocilizumab-treated xenograft tumors Fig. S12 demonstrates the changes in STAT3 and ERK target gene expression in xenograft tumors in response to tocilizumab treatment Table S3 provides details on the antibodies used for IHC staining Table S4 provides details of linear regression analysis of ESCC and EAC tumor growth kinetics in response to tocilizumab Table S5 provides details of linear regression analysis of HNSCC and gastric cancer tumor growth kinetics in response to tocilizumab Table S6provides details of the mixed effect linear mix model analysis of changes in STAT3 and ERK target gene expression in response to tocilizumab