medwireNews: Paired analysis of primary and relapsed breast cancer specimens shows that many HER2-negative patients switch between HER2-low and HER2-0 expression during disease progression.
The research was presented at the ESMO Breast Cancer Virtual Congress 2021 by Federica Miglietta, from the University of Padova in Italy, who reported findings for 547 patients who were initially treated for breast cancer between 2007 and 2013.
Overall, 45% of primary and 49% of relapse disease samples that were initially classified as HER2-negative were further described as being HER2-low, on the basis of immunohistochemistry and in situ hybridisation amplification.
HER2-low expression was “highly unstable during disease evolution,” Miglietta said. There was a 39% discordance in the HER2 status between primary and relapse tissue samples that was explained by 15% of patients switching from HER2-0 to HER2-low expression and 14% from HER2-low to HER2-0 expression, while 10% of patients gained or lost HER2-positive status between biopsies.
Miglietta noted that discordance between samples was more likely among patients with hormone receptor-positive, HER2-negative disease than among triple-negative breast cancer patients (45 vs 37%), with a change in HER2-low to HER2-0 status or vice versa accounting for 40% and 31% of the discordance in these subtypes, respectively.
She concluded that the findings “stress the importance to retest HER2 expression at relapse since it may open new therapeutic opportunities in a not negligible proportion of HER2-negative breast cancer patients and better assist clinicians in the selection of patients treatable [with] novel anti-HER2 strategies in the context of clinical trials.”
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