Binding analysis on the colon carcinoma cell line LIM1215 (~ 20,000 HER3/cell), HCT116 (< 1900 (1520) HER3/cell) and SW-620 (< 1900 (1160) HER3/cell), the breast cancer cell lines MCF-7 (~ 18,000 HER3/cell), BT-474 (~ 11,000 HER3/cell) and the pharynx carcinoma cell line FaDu (~ 3000 HER3/cell) revealed superior binding for the scDb-scFv compared to scDb, due to the avidity effect of this molecule. The gene discussed is ERBB3; the disease is breast carcinoma.