Would you consider dual anti-HER2 therapy for a perimenopausal woman found to have multifocal pT1mic pN1mic HER2+ HR- breast cancer following a bilateral mastectomy for DCIS?

The optimal treatment for DCIS with microinvasion DCISm is not fully established. There is a nice analysis and discussion from Si et al., PMID 33344258 outlining the factors for worse outcomes. Her multifocality, ER-HER2+ status, and most importantly, nodal involvement increases her risk compared to...

Dual therapy will be over treatment.

Agree with APT.

Of the 406 women in the APT trial (Tolaney et al., PMID 25564897), 9 (2.2%) had T1mic disease and 6 (1.5%) had N1mic disease. These are very low numbers and it is unlikely that patient had both characteristics. Given the extremely low recurrence rates with the APT regimen (not dual anti-HER2 therapy...