Pancreatic cancer has one of the worst prognosis of any malignant disease. The National Registry of Japan Pancreas Society has reported that only 13% of patients achieve 5 years survival after surgical resection. The vast majority of patients present with metastatic or unresectable disease. Gemcitabine (GEM) has replaced 5-fluorouracil (5-FU)-based chemotherapy as the standard of care. GEM first generated improvements in symptom control and survival in advanced disease, spurring further research. For locally advanced disease, most recent studies have incorporated GEM into combined-modality therapy. However, subsequent trials have not demonstrated that combinations of other agents with GEM extend clinical benefits yet. Similarly, in surgically resectable disease, current trials are incorporating GEM into adjuvant therapy. According to several clinical trials it has been demonstrated that improvements in locoregional control and survival may be achieved when chemotherapy using 5-FU is added to radiation for locally advanced pancreatic cancer. The new regimen for locally advanced disease has demonstrated that the better outcome is expected by chemoradiation therapy with 5-FU followed by GEM treatment. Furthermore, one of the patients showed the significant regression of pancreas tumor, resulting in the successful surgical resection. In order to develop chemotherapy for pancreatic cancer, we are analyzing mRNA expression of pancreas cancer cell lines and examined their resistant against to GEM. One of the genes is demonstrated to be a responsible for drug sensitivity by clustering analysis.