Because we found that piR-35127 and piR-46545 were down-regulated in lung cancer cells over-expressing RASSF1C and were also down-regulated in 50% of lung tumor tissues examined, we over-expressed piR-35127 and piR-46545 in lung and breast cancer cell lines and in normal lung and breast epithelial cells and assessed their impact on cell proliferation, colony formation, and apoptosis. The gene discussed is PIR; the disease is lung cancer.