To evaluate whether the FRβ-expressing myeloid cells in a tumor mass might bind folic acid, 4T1 murine breast cancer cells were implanted in immune competent Balb/c mice and resulting tumors were dissociated into component cells prior to incubation with a folic acid conjugate of the fluorescent dye Cy5 (FA-Cy5). The gene discussed is FOLR2; the disease is breast carcinoma.