ERBB2/HER2 alterations were identified in 5 pmucBC (23 %): ERBB2 amplification was found in 3 of 3 cases (100 %) that were HER2+ by IHC and/or FISH; 1 pmucBC was negative for HER2 overexpression by IHC, but positive for amplification by CGP; and 2 pmucBC harbored the ERBB2 substitutions D769Y and V777L (one sample also featured ERBB2 amplification).