The fact that levels of active TGFβ are elevated in tumors grown in SPARC−/− animals and that losartan decreases TGFβ activity supports the concept that excess TGFβ1 participates in the accelerated tumor progression and altered tumor microenvironment of orthotopic Pan02 tumors grown in the absence of host SPARC. The gene discussed is TGFB1; the disease is neoplasm.