An experimental therapy has shown a high response rate and help shrink tumors in lung cancer patients with a specific form of genetic alteration, according to a clinical trial unveiled Saturday. The Pfizer Inc. drug crizotinib shrank tumors in lung cancer patients with advanced non-small cell lung cancer (NSCLC) with a specific gene alteration of an enzyme implicated in cancer cell growth, known as anaplastic lymphoma kinase, or ALK. According to Pfizer, around 10,000 people in the United States are affected by a lung cancer with this particular genetic mutation. About 90 percent of the 82 participants in the small-scale Phase I clinical trial responded positively, and more than half -- 57 percent -- saw their tumors shrink after eight weeks, said lead author Yung-Jue Bang, a physician at Seoul National University College of Medicine. Researchers had only expected about 10 percent of the patients, many of whom had already received three or more prior treatments, to respond to the treatment. 'These results are quite dramatic, and represent an important improvement over what we would see with standard chemotherapy for patients with metastatic disease,' Bang told a news conference. Most of the NSCLC patients were former smokers or never smoked. The median duration of treatment was approximately six months. Crizotinib, which is taken orally, works by inhibiting the ALK enzyme. About one in 20 lung cancer patients in the United States are estimated to be diagnosed with ALK-positive NSCLC each year. The genetic variation targeted by crizotinib affects about five percent of lung cancer patients. Each year, 12 million new cases of lung cancer are diagnosed worldwide and nearly eight million people die from the disease. The study was presented at the American Society of Clinical Oncology conference, which is being held in Chicago this weekend. Pfizer has begun a late-stage, or Phase III, trial to determine whether crizotinib improves the survival rate of ALK-positive lung cancer patients compared to standard chemotherapy treatment. 