The present invention provides for identification of agents that induce
growth arrest and survival of cancer cells, which remain dormant in bone
marrow, thus preventing their eradication through use of standard
chemotherapy or radiation therapy. Basic fibroblast growth factor
(FGF-2), a mammary differentiation factor abundant in the bone marrow
stroma, induces growth arrest of relatively differentiated breast cancer
cells and restricts their survival to fibronectin by upregulating
integrin .alpha.5.beta. 1. Most of the FGF-2-arrested cells fail to
establish optimal ligation to fibronectin and undergo cell death. Cells
that do attach to fibronectin, another major constituent of the bone
marrow microenvironment, stay alive and growth-arrested for many weeks.
Using function-blocking antibodies and peptides, a specific contribution
of .alpha.5.beta.1-fibronectin interaction in maintaining survival of
growth-arrested cells was demonstrated. The present invention thus allows
for methods, agents and pharmaceutical compositions that can be used to
potentiate the activity of chemotherapy or radiation therapy.