Would you include the supraclavicular basin in adjuvant radiation treatment fields if there were multiple positive axillary sentinel lymph nodes with ECE discovered at the time of resection of a proximal arm cutaneous SCC?   

Short answer, I wouldn't. I'd do good restaging (PET vs contrasted CT or both) and ensure you're just dealing with microscopic residual or to guide boosting to gross disease dose if gross residual in axilla, and just treat your involved axilla and primary site if indicated. This is a patient who wou...

"Historically," pre-immunotherapy, when post-op radiation was used more commonly, the supracalv would be treated electively. However, maybe not as important to do now as suggested by Dr. @Whitaker. I still elect to radiate the supraclav for this clinical situation. 

Probably not. I agree that evaluating the supraclavicular basin carefully with imaging is a good idea. The most relevant data I am aware of that suggests that treating the supraclavicular basin is not necessary for a skin cancer with axillary metastases. A retrospective, observational study of cutan...

I would favor RNI to level 1 to 3 and the medial supraclavicular area.