Given its ability to reduce primary tumor burden and block BMP9-induced tumor cell proliferation in vitro and in vivo, we assessed the effects of ALK1Fc on the relative expression of ALDH1A1, a marker previously associated with cancer stem cell-like properties and poor patient prognosis (Li et al., 2010; Le Magnen et al., 2013). The gene discussed is ALDH1A1; the disease is cancer.