ACVR1 and fibrodysplasia ossificans progressiva: Although a recent study indicated that anti-ACVR1 monoclonal antibodies promoted HO in FOP mouse models and thus should not be pursued as a treatment strategy for FOP (Aykul et al. 2022), Kan et al. (2019) demonstrated that ICIs prevented HO in animal models, highlighting the potential importance of these drugs in the context of FOP.