Activation of the ras/raf signal transduction pathway has been shown to be involved in many proliferative and developmental signals as well as in transformation and tumorigenicity of many types of cancers (1 -4) . However, small cell lung cancer (SCLC) cell lines, and SCLC in patients, rarely possess ras mutations (5) . In these cancers, ras mutations may not confer a growth advantage. In fact, in SCLC cell lines, introduction of an activated ras gene results in cell differentiation accompanied by slower cell growth (6) .
