Stage 4 lung cancer
which has spread to brain has a very poor prognosis.
Palliative RT to brain may relieve some symptoms.
If his type of cancer is adenocarcinoma then a particular test called EGFR mutation test from biopsy block may be of help.
If EGFR mutation is positive then oral chemotherapy
Erlotinib ,Gefitinib can be given even in poor general condition of the patient.
The main side effects of Erlotinib and gefitinib is skin rash and diarrhea which can be managed with lactocalamine lotion and loperamide
The development of skin rash is good prognosis.
For mood swings u can give haloperidol