Study on the state of implementation of HER2 testing and positive ratios in patients with breast cancer in the Kyushu-Okinawa region of Japan

Abstract

The development of molecular-targeted agents has improved the recovery rate for cancer. In Japan, trastuzumab has been approved as an adjuvant treatment for human epidermal growth factor receptor-2 (HER2)-positive breast cancer; therefore, accurate management of HER2 testing has become more important. In addition, proper patient selection is required from the viewpoint of health care economics. The current situation of HER2 testing in patients with infiltrating breast cancer from April 2008 to March 2009 was evaluated in 49 institutions (50 departments) treating breast cancer in the Kyushu-Okinawa region. In a total of 5286 samples, HER2-positive ratio was 14.2%, which may reasonably reflect the current state of HER2 testing for breast cancer in the Kyushu-Okinawa region. There was a moderate discrepancy in HER2-positive ratio between institutions. Immunohistochemistry (IHC) analysis was outsourced in 15 institutions, and fluorescence in situ hybridization (FISH) analysis was outsourced in 23 institutions. The ratio of retesting by FISH analysis for samples judged as 2+ on IHC was 86.1%. There was no correlation between HER2-positive ratio and the number of HER2 tests at the institution. However, a high percentage of HER2 IHC 0-1+ results and a low percentage of HER2 2+ and 3+ results at the institution were significantly correlated with a high percentage of HER2 FISH-positive results for HER2 IHC 2+ cases. There is a moderate discrepancy in HER2-positive ratio between institutions. Institutions with a high percentage of HER2 IHC 0-1+ and a low percentage of HER2 2+ and 3+ may have more false negative cases. These institutions should perform internal accuracy evaluations in order to maintain proper diagnostic judgment.