['The aim of this study was to evaluate the efficacy and safety of irinotecan monotherapy in patients with advanced pancreatic cancer (APC).', 'Patients with APC refractory to gemcitabine and S-1 were included. Irinotecan (100 mg/m(2)) was administered on days 1, 8, and 15 every 4 weeks until disease progression or unacceptable toxicity was observed. The relationship between uridine diphosphate glucuronosyl transferase 1 family polypeptide A1 gene (UGT1A1) polymorphisms and clinical outcomes was evaluated.', 'Between January 2007 and December 2011, 231 cycles were delivered in 56 patients. Irinotecan was administered as second-line chemotherapy in 35.7% of patients and as third-line chemotherapy or later in 64.3%. A partial response was achieved in two (3.6%) and stable disease in 23 patients (41.0%), giving a disease control rate of 44.6%. The median time to progression (TTP) and overall survival (OS) were 2.9 (95% confidence interval [CI] 1.8-3.5) months and 5.3 (95% CI 4.5-6.8) months, respectively. Median survival from the first-line chemotherapy was 19.5 (95% CI 15.3-23.8) months. Major grade 3/4 adverse events included neutropenia (28.6%), anemia (12.5%), and anorexia (10.7%). Patients with *6 and/or *28 allele(s) (n = 15) were associated with grade 3/4 neutropenia and anorexia but showed longer TTP (5.3 vs. 1.8 months; p = 0.05), and OS (8.0 vs. 4.8 months; p = 0.09) than those without *6 and/or *28 (n = 29).'] Are uridine diphosphate glucuronosyl transferase 1 family polypeptide A1 gene ( UGT1A1 ) polymorphisms associated with toxicity and efficacy in irinotecan monotherapy for refractory pancreatic cancer?