What evidence supports the use of high tangents for pN1mic breast cancer?

This is a great question. To add to the excellent answers from @Dr. First Last and @Dr. First Last, here are some of my thoughts on this topic:

At the time of MA.20, the size of nodal metastasis was not routinely measured so it is unclear what percent of patients in MA.20, if any, had micrometastases...

There are limited prospective or randomized data looking at only N1mic patients outside the IBCSG trial (Galimberti et al., PMID 23491275) and in that trial, RT was a bit heterogeneous (some got no RT, some IORT). The study does demonstrate the risk of additional nodes for patients with pN1mic disea...

This is an interesting question, and another variation is pN1mi in the setting of patients who undergo mastectomy, where we do not usually consider high tangents and typically advocate for PMRT if there are additional risk factors.

I believe the addition of pN1mi for eligibility into MA.39 was off o...