RSPO1 and neoplasm: However, no trend toward a gradual increase in the interaction density was observed between POSTN+ fibroblasts and FOLR2+ macrophages or between SPP1+ macrophages and RSPO1+ fibroblasts, indicating the specificity of the cellular interactions among POSTN+ fibroblasts, SPP1+ macrophages and tumor cells during the multistep progression of HNSCC.