Background and purpose: Uridine diphosphoglucu-ronosyl transferase 1A1 (UGT1A1) is an important enzyme for metabolism of irinotecan. The activity of UGT1A1 enzyme was significantly affected by the gene polymorphism. This study aimed to investigate the correlation of UGT1A1*28 and *6 gene polymorphisms with irinotecan-based chemotherapy in colorectal cancer(CRC). Methods: Analysis of UGT1A1*28 and *6 gene polymorphisms was performed in 160 gastrointestinal cancer patients admitted to Zhongshan Hospital Fudan University from Apr. 2013 to Dec. 2013 by amplifying the gene fragments using PCR

STR and Sanger sequencing. Eighty-two cases with CRC treated with irinotecan were chosen to observe the adverse events during chemotherapy. The incidence of different genotypes was compared. Results: The distribution of the genotypes in 160 gastrointestinal cancer patients was as followed: UGT1A1*28 wild-type genotype TA6/6 (124

77.5%)

heterozygous genotype TA6/7 (33

20.5%)

and homozygous genotype TA7/7 (3

2.0%); UGT1A1*6 wild-type genotype GG (105

65.6%)

heterozygous genotype GA (48

30.0%)

and homozygous genotype AA (7

4.4%). In the 82 CRC cases

the incidences of grade 3 and 4 neutropenia in the patients carrying UGT1A1*28 (TA6/7+ TA7/7 ) were higher than those in the WT genotype (TA6/6) (58.3% vs 0.0

P0.001)

and increased the total incidence of adverse events (76.0% vs 45.6%

P0.001). There was no significant relevance between UGT1A1*6 genotype

age

gender chemotherapy and adverse events. Conclusion: In the CRC cases with irinotecan-based chemotherapy

the UGT1A1*28 (TA6/7+TA7/7) genotype significantly increased the risk of grade 3 and 4 neutropenia. Detecting UGT1A1 gene polymorphisms may guide individualized treatment and predict adverse events.