Human epidermal growth factor (HER2)-negative primary breast tumours may evolve to express low HER2 upon relapse, highlighting the need to retest recurrent tumours for HER2 expression, researchers say.

“The results provide a whole new insight on how HER2-low tumours might evolve as a subgroup, possibly challenging the current dichotomy between HER2-positive and HER2-negative breast cancer,” Dr Federica Miglietta, of the University of Padua in Italy, said in a statement from the ESMO Breast Cancer Virtual Congress, where the findings were presented.

In the study, matched samples of primary and relapse breast cancers from 547 women were assessed for HER2 status according to the American Society of Clinical Oncology/College of American Pathologists recommendations in place at the time of diagnosis (2007-2013), with a 10% cut-off for immunohistochemistry applied.

HER2-negative cases were subclassified as HER2 low and HER2 negative.