DNA Topoisomerase I Gene Copy Number and mRNA Expression Assessed as Predictive Biomarkers for Adjuvant Irinotecan in Stage II/III Colon Cancer

Abstract

Purpose: Prospective-retrospective assessment of the TOP1 gene copy number and TOP1 mRNA expression as predictive biomarkers for adjuvant irinotecan in stage II/III colon cancer.Experimental Design: Formalin-fixed, paraffin-embedded tissue microarrays were obtained from an adjuvant colon cancer trial (PETACC3) where patients were randomized to 5-fluorouracil/folinic acid with or without additional irinotecan. TOP1 copy number status was analyzed by fluorescence in situ hybridization (FISH) using a TOP1/CEN20 dual-probe combination. TOP1 mRNA data were available from previous analyses.Results: TOP1 FISH and follow-up data were obtained from 534 patients. TOP1 gain was identified in 27% using a singleprobe enumeration strategy (4 TOP1 signals per cell) and in 31% when defined by a TOP1/CEN20 ratio 1.5. The effect of additional irinotecan was not dependent on TOP1 FISH status. TOP1 mRNA data were available from 580 patients with stage III disease. Benefit of irinotecan was restricted to patients characterized by TOP1 mRNA expression third quartile (RFS: HR adjusted , 0.59; P ¼ 0.09; OS: HR adjusted , 0.44; P ¼ 0.03). The treatment by TOP1 mRNA interaction was not statistically significant, but in exploratory multivariable fractional polynomial interaction analysis, increasing TOP1 mRNA values appeared to be associated with increasing benefit of irinotecan.Conclusions: In contrast to the TOP1 copy number, a trend was demonstrated for a predictive property of TOP1 mRNA expression. On the basis of TOP1 mRNA, it might be possible to identify a subgroup of patients where an irinotecan doublet is a clinically relevant option in the adjuvant setting of colon cancer. Clin Cancer Res; 22(7); 1621-31. Ó2015 AACR.

An Explorative Analysis of ABCG2/TOP-1 mRNA Expression as a Biomarker Test for FOLFIRI Treatment in Stage III Colon Cancer Patients: Results from Retrospective Analyses of the PETACC-3 Trial

“…In a previous study, which included the 580 PETACC-3 patients [5], we found in Stage III CC patients a trend towards association between high ABCG2 expression and poor patient outcome in the irinotecan containing treatment group, but not in the 5FUL only treated group. In another retrospective PETACC-3 study [7], we reported for low TOP1 expression a trend towards an association with short RFS and a borderline significant association with shorter OS in the irinotecan treated patients but not in the 5FUL treated patients [7]. On the assumption that more than one molecular resistance mechanism is involved in irinotecan resistance [5], we now combined ABCG2 and TOP1 expression status in a single dichotomous parameter and hypothesized that patients with a tumor with a high ABCG2 and a low TOP1 expression level might represent those with a low response to irinotecan added to adjuvant 5FUL treatment.…”

“…For ABCG2, the median from the whole expression data set (Stage II and III) was chosen to dichotomize the patients into ABCG2 high and ABCG2 low. For TOP1 mRNA, we used, based on our previous study [7], the third quartile on the whole expression data of stage II and III patients to group the patients into TOP1 high and low. ABCG2 and TOP1 were then combined into a binary variable: ABCG2 high (above median) and TOP1 low (below the 75-percentile) formed the "resistant patients", while all other combinations of ABCG2 and TOP1 formed the "sensitive patients ".…”

“…For a detailed description, including a CONSORT diagram on the selection of the present PETACC-3 cohort, please see [7]. Table 1 shows the clinicopathological characteristics of the n = 580 stage III CC patients included in the study.…”

“…Of specific interest is that the resistance mechanisms in our three oxaliplatin-resistant colorectal cancer cell lines [5] did not include regulation of ABCG2 or TOP1 mRNA. In recent publications [5,7], we correlated each of ABCG2 and TOP1 mRNA expression to patient outcome in a subset of Stage III colon cancer patients enrolled in the PETACC-3 study. A trend was demonstrated towards high ABCG2 mRNA expression being correlated with shorter recurrence-free survival (RFS) and shorter overall survival (OS) when compared to patients with low ABCG2 mRNA expression [5], and high TOP1 expression was significantly associated with longer OS but not RFS in FOLFIRI treated patients [7].…”

“…In recent publications [5,7], we correlated each of ABCG2 and TOP1 mRNA expression to patient outcome in a subset of Stage III colon cancer patients enrolled in the PETACC-3 study. A trend was demonstrated towards high ABCG2 mRNA expression being correlated with shorter recurrence-free survival (RFS) and shorter overall survival (OS) when compared to patients with low ABCG2 mRNA expression [5], and high TOP1 expression was significantly associated with longer OS but not RFS in FOLFIRI treated patients [7]. We now hypothesize that low TOP1 and high ABCG2 expression ("resistant patients") define patients who will not benefit from irinotecan containing adjuvant chemotherapy while any other combination of these two genes defines patients ("sensitive patients") who will benefit from the addition of irinotecan to 5FUL.…”