What would be your next line of treatment for NSCLC adenocarcinoma that has recurred after chemoradiation with cis/etoposide?

In this setting, it would depend upon the timing from completion of definitive chemoradiation and relapse/progression. In the absence of more definitive data, I take my cue from what most "first line" clinical trials have used for their eligibility criteria - patients are candidates (typically) if their prior chemoradiation (or, for that matter, adjuvant chemotherapy) was completed six months or more prior to documentation of recurrence. For this reason, if < 6 months, I would probably treat as "second line" and use either Nivolumab, Atezolizumab or (if PDL1 between 1 and 49%), Pembrolizumab. If more than six months have elapsed, then I would use, as suggested in the question, Carbo/Pemetrexed/Pembrolizumab.

Though not part of the question...