ERBB2 and neoplasm: There was no apparent benefit in tumours with HER2 to CEP17 ratios below the 2·0 threshold for HER2 positivity, consistent with the reduced efficacy of trastuzumab in low HER2 tumours in the NSABP trial B-47;19 however, there were not enough patient numbers to assess whether, for example, 1·8 or 2·2 might be a better cutoff for HER2 positivity than might 2·0.