To find out if sema3A, sema3D, sema3E, sema3F or sema3G over-expression can affect the development of tumors from different tumorigenic cell lines, we expressed the full length cDNAs encoding the five semaphorins or an empty control vector in the tumor cells using a lentiviral expression vector that confers resistance to puromycin. The gene discussed is SEMA3F; the disease is neoplasm.