e14560 Background: UGT1A1*6 as well as UGT1A1*28 polymorphisms is associated with decreased glucuronidation of SN-38, the active metabolite of irinotecan (CPT-11). Although the maximum tolerated dose (MTD) and the recommended dose (RD) in Hetero was determined 150 mg/m2 (approval dose in Japan), those of Homo were unknown. Methods: Pts received prior chemotherapies except for CPT-11 for metastatic gastrointestinal cancer were enrolled. UGT1A1 polymorphisms were categorized into Wild(*1/*1), Hetero(*1/*28, *1/*6), and Homo(*28/*28, *6/*6, *28/*6). CPT-11 was administered biweekly. Starting doses were 150 mg/m2 in Wild, 100 mg/m2 in Hetero, and 75 mg/m2 in Homo. DLT was defined as grade 4 hematological, or grade 3 non-hematological toxicity. MTD closest to dose-limiting toxicity (DLT) appearance of 30% was guided by the continual reassessment method in the cohort of Hetero and Homo. DLT and pharmacokinetic (PK) sampling was evaluated during the 1st cycle. Results: Eighty-two pts were enrolled from November 2006 to November 2008 (Wild, Hetero, Homo: 41, 20, and 21, respectively). The dose level reached at 150 mg/m2 in Homo. At 150 mg/m2, DLT was observed in six pts of Homo (grade 4 neutropenia, grade 3 diarrhea: 6 and 1, respectively). The probability of DLTs were 22.2% at 125 mg/m2, and 37.4% at 150 mg/m2. The MTD was determined 150 mg/m2 in pts with Homo group. However, the incidences of grade 3/4 neutropenia at 150 mg/m2 during the 1st cycle were 9.8% (4/41), 18.8% (3/16), and 62.5% (10/16) in Wild, Hetero, and Homo, respectively. And the second administration was delayed 7 days or more in most pts in Homo (63% at 150 mg/m2). In one pt of Homo for *28/*28 died of septic shock during the 2nd cycle. SN-38 AUC (0–24h, ng*hr/mL, median) was 239 in Wild, 237 in Hetero, and 410 in Homo. Pts with Homo showed the different trend of PK/PD compared to those with Wild and Hetero. Conclusions: The MTD was 150 mg/m2 in pts with Homo group and the most frequent DLT was grade 4 neutropenia. However, our findings suggest that 150 mg/m2 q2w is difficult to recommend and the initial dosage and administration should be considered carefully for pts with Homo. [Table: see text]
How to design a dose-finding study using the continual reassessment method
