title: ABCG2 expression in colorectal adenocarcinomas may predict resistance to irinotecan.
abstract: Irinotecan is a key drug for patients with advanced and recurrent colorectal carcinoma. However, the efficacy of irinotecan is not sufficient; partly, as there is no useful marker to predict chemosensitivity to the drug. The aim of the present study was to evaluate whether the expression levels of adenosine triphosphate-binding cassette sub-family G (WHITE) member 2 (Junior blood group) (ABCG2) in primary colorectal tumors predict chemoresistance to irinotecan. Using the resected primary tumor specimens of 189 patients with colorectal cancer, the association between the immunohistochemical expression of ABCG2 protein and the results of the collagen gel droplet embedded culture drug sensitivity test, performed to evaluate the chemosensitivity to SN-38 (an active metabolite of irinotecan), was investigated. Among the 189 patients, 17 received irinotecan-based chemotherapy, and their responses and progression-free survival (PFS) were analyzed. The tumors of patients with increased ABCG2 expression accounted for 60% of the tumors examined, and were significantly more resistant to SN-38, compared with patients with low ABCG2 expression (P<0.001). In a multivariate logistic regression analysis, increased expression of ABCG2 protein was an independent and significant predictor of resistance to SN-38, increasing the risk of resistance by 12-fold. Increased expression of ABCG2 and a low sensitivity to SN-38 was significantly associated with resistance to irinotecan-based chemotherapy (P=0.01 and 0.028, respectively). The median PFS of patients with increased expression of ABCG2 was significantly shorter, compared with patients with low expression levels of ABCG2 (104 vs. 242 days; P=0.047). The increased immunohistochemical expression of ABCG2 in primary tumors may be a useful predictive biomarker of resistance to irinotecan-based chemotherapy for patients with recurrent or metastatic colorectal cancer.
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Hoang Dinh
authors.initials: HD
authors.lastname: Tuy
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Shiomi
authors.affiliation: Department of Pathology, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Ken Ichi
authors.initials: KI
authors.lastname: Mukaisho
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Naka
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Tomoharu
authors.initials: T
authors.lastname: Shimizu
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Sonoda
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Eiji
authors.initials: E
authors.lastname: Mekata
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Endo
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Kurumi
authors.affiliation: Department of Pathology, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sugihara
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Masaji
authors.initials: M
authors.lastname: Tani
authors.affiliation: Department of Surgery, Shiga University of Medical Science, Otsu, Shiga 520-2192, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Tani
keywords: ABCG2; colorectal adenocarcinoma; drug resistance; irinotecan