Would you offer radiation to the contralateral breast if after neo-adjuvant chemo and prophylactic contralateral mastectomy yielded ITC only in a single lymph node and no breast primary?

Other factors would influence my decision. What was the burden of disease for starting NACT on ipsilateral side?

Could this be spread from the contralateral breast to the lymph node?

Was MRI imaging done prior to chemo?

Did staging show any enlarged contralateral node?

Pre-treatment work-up/findings...

Based on description with many high risk factors it looks like contralateral spread from high nodal burden on ipsilateral side. The outcome is poor with a high nodal burden, even after chemo. I may consider treating contralateral axilla and s/c along with comprehensive PMRT on same side.