ACVR1B and neoplasm: For example, CX3CR1+ macrophages in SF1-lineage tumors play a nuanced role of immune cells in tumor apoptosis via INHBA-ACVR1B signaling.13 CD8+ T cell infiltration is notably prevalent in growth hormone-secreting adenomas (GHomas), correlating negatively with tumor aggressiveness and predicting better responses to somatostatin analogs.16,17 Conversely, tumor-infiltrating T cells in SF1-lineage gonadotrophs promote immune evasion through the release of immunosuppressive cytokines such as IL-1018.