How would you treat a young breast cancer patient with limited nodal involvement and an isolated sternal oligometastasis at diagnosis?

Although there is limited data to support this approach, I have treated similar patients with "curative intent" with respect to the RT portion of their treatment.

If the sternal oligomet is in close proximity to the ipsilateral IMNs, it can be included within the partial wide tangent fields for the "initial" portion of the treatment course (e.g. 50 Gy) without any additional fields needed. I would boost the oligomet (as a site of undissected gross disease) to a dose of 66 Gy (or higher, if OARs allow), and this boost can usually be achieved either with en face electrons or IMRT, depending on the depth, location, etc. An alternative would be to SBRT the sternal oligomet, delivered either before or several weeks after the breast + cRNI portio...

Agree with the approach of Dr @Dr. First Last. In appropriately selected and motivated patients, definitive intent therapy (as suggested above) can be considered. Here is an example of a single institutional experience regarding such a scenario.

Christopherson et al., PMID 30851348

This should probably be discussed in the context of the multiple recently reported breast MDT trials which were not as auspicious, however.

A "sternal oligometastasis" is probably not a true oligometastasis but rather internal nodal involvement and as such has a better prognosis than the usual oligometastasis. I favor reasonably aggressive local regional treatment preferably with concurrent chemotherapy, e.g.capecitabine.