ACVRL1 and neoplasm: Interestingly, our short-term trial in the 4T1 model corroborates the trends observed in trials with a longer duration but expanded on the role of ALK1 in the mobilization of monocytes, as evinced by the evidently lower relative number of macrophages in tumor-free hosts in the ALK1-Fc cohort compared with the IgG2a control cohort.