Keytruda progression?

An update about my dad who was diagnosed with Stage 4 NSCLC last Feb. So, he had 4 cycles of Carboplatin+Permetrexed last Feb-Apr 2025 and since there was progression after the 4th cycle, his treatment was changed to Keytruda alone.

He did Keytruda alone for 3 cycles and after the 3rd cycle his scans showed progression everywhere. Our onco then decided to add Paclitaxel to his Keytruda and just last Dec, his scans showed almost complete regression of all tumors (just one stubborn one left). He finished 6 cycles of Paclitaxel last Jan and now he's back on Keytruda alone.

His scans yesterday are suddenly showing new nodules and there's also a possibility of brain mets. He is also in so much pain right now that we had to bring back his fentanyl patch (this was already removed last Dec) and we also had to put him on 2 more pain meds. I'm really thinking that Keytruda alone is not working for him, I don't know how else to convince his onco about this since they're still planning to push through with his immunotherapy on Monday. Has anybody experienced this as well?