Although, the binding of the Bi-FAP/mEnd-IL to the vascular endothelia of mice lungs, liver and kidneys was related to the overexpression of murine endoglin and hence contributed to an overall comparable tumor fluorescence levels to that seen with FAP-IL, a more suitable and reliable tumor imaging based on the simultaneous targeting of human endoglin and human FAP should be expected. The gene discussed is FAP; the disease is neoplasm.