This is an interesting question. Recently in the NEJM (July 2018) there was a phase 1/2 study using an anti PD1 agent (cemiplimab) for advanced, unresectable or metastatic cutaneous squamous cell carcinoma. Previously this was a tumor type with no approved therapies and treatment...

I usually use cetuximab/carboplatin/5fu as 1st line therapy if pt is fit.  if not, then single agent cetuximab or weekly platinum. There is not much data but mostly extrapolation from head/neck cancer.   For 2nd line therapy, I try to use pd-1 or pd-l1 inhibitor which would be off-label u...