Would you give chemotherapy and trastuzumab to a patient with multifocal high grade, microscopic (<5 mm) HR-, HER2+ IDC embedded in extensive DCIS, staged as pTis pT1a(m) N0?

The data is limited, especially in extensive high grade DCIS with microinvasion that is HER2 positive and the decision must build on the balance of benefit vs risk of treatment.

In extensive DCIS with multifocal T1a as described in this question, I don't hesitate to recommend adjuvant chemotherapy wi...