HER2 few recurrences.

Top Line: Does concurrent trastuzumab reduce recurrence risk among patients receiving whole breast radiation for HER2+ DCIS?

The Study: HER2 overexpression is not uncommon in DCIS. Yet, HER2 status does not currently alter treatment for DCIS, and HER2 testing is not frequently performed. In B-43, tissue specimens from 7888 eligible patients treated with lumpectomy for DCIS were submitted for HER2 testing. Of these, 35% (2014) were HER2 positive. They were randomized to receive whole breast radiation (either conventional or hypofractionated) with or without concurrent trastuzumab followed by endocrine therapy as indicated. Trastuzumab was given in 2 doses: once at the start of RT (8 mg/kg) and again 3 weeks later (6 mg/kg). There was no maintenance trastuzumab. Most patients were < 60 (62%) and had high grade DCIS (83%). Just over half (58%) were hormone receptor positive. After a median follow-up of 79 months, there was no difference in the rate of ipsilateral breast tumor recurrence between RT alone (6.3%) and RT+T (5.1%). Of note, there were much fewer IBTR events than planned for statistical analysis, and the 19% relative reduction in IBTR did not exceed the pre-specified 36% reduction. One third of IBTR events were invasive while ⅔ were non-invasive. This is quite different from the 50/50 rule of thumb we typically learn. Finally, there were no significant toxicity concerns with the two trastuzumab doses.

TBL: The addition of concurrent trastuzumab to whole breast radiation does not significantly reduce the risk of breast tumor recurrence among patients with HER2+ DCIS. | Cobleigh, J Clin Oncol 2021