Result of HER2 status in Japanese metastatic gastric cancer: Prospective cohort study (JFMC44-1101).

Abstract

10 Background: Randomized phase III (ToGA trial) has demonstrated that the addition of trastuzumab to standard chemotherapy improved overall survival in patients (pts) with HER2-positive metastatic gastric cancer (mGC). In screening of the ToGA trial, HER2 positivity rate was 22.1 % in total, but the rates varies between countries. Therefore, to determine the HER2 incidence rate in Japanese mGC, we planned prospective cohort study JFMC44-1101. Methods: JFMC44-1101 is a multicenter epidemiological trial assessing HER2 status in Japan. Patients with histologically confirmed gastric adenocarcinoma, not suitable for curative resection were eligible. HER2 status was centrally assessed both immunohistochemistry (IHC) and fluorescence in-situ hybridization (FISH) using formalin fixed paraffin embedded (FFPE) tissues from tumor. HER2 positive is defined as either IHC3+ or FISH+ in accordance with ToGA trial. Overall and subgroup estimates calculated with 95%CI. Results: Between September 2011 to June 2012, 1466 pts were registered from 157 sites. Patients characteristics were; gender (M/F):1044/422, median age (min-max): 68 (25-99), advance / recurrence: 1068 / 398. Samples are 768 from biopsy and 698 from excision. In August 2012, 1427/1466 pts were assessed. Overall, HER2 positivity was 20.5% (293 pts). Each IHC status (0/1+/2+/3+) with FISH+ was 3.0% / 11.3% / 46.9% / 97.2%, respectively. The frequency of IHC 0/1+ with FISH+ was almost as high as IHC 2+ with FISH+ (5.6%/4.2%). HER2 positivity rate of background factors were; male/female:23.6%/14.3%, biopsy/ excision: 22.7%/19.0%, advance / recurrence: 21.6%/17.6%. Conclusions: JFMC44-1101 confirmed the incidence of HER2 positivity in Japanese mGC. HER2-positivity rate and HER2 status were similar to the ToGA screening population. Clinical trial information: UMIN000006190.