Clinical guidelines typically suggest padcev + keytruda at this stage. The good news: it can be highly effective. My oncologist stated 30% "cure" rate. Many with complete response will proceed to keytruda only (less severe side effects). The bad news: padcev especially can be highly toxic with neuropathy, loss of taste and smell, severe fatigue, nausea, skin lesions and other problems , loss of eyesight and worse. Padcev is targeted medicine: it targets cancer cells with NECTIN expression and delivers a highly toxic payload. Keytruda is a PDL1 blocker immunotherapy. Similar to avelumab and nivolumab. Atezolizumab is rarely used anymore for bladder cancer and not for stage 4 I believe but I could be wrong.

Unfortunately, bladder adenocarcinoma is exceedingly rare (< 2% of cases) and as such treatments are more experimental as there are few to no clinical studies on it as it is near impossible to recruit patients due to its rarity.