Man wants full treatment

A patient with end-stage Lung Cancer and developmental delay has been hospitalized repeatedly for aspiration pneumonia, requiring mechanical ventilation. He lacks decision-making capacity, and there is nobody close to him that can serve as a surrogate decision-maker. Full-treatment of the cancer can extend his life a little, but he will die from his disease. Treatment also causes him pain, which can’t be controlled without threatening his life. The man insists on full treatment, but is also very agitated by the pain. The care team wonders if they should cease treatment of the cancer in order to provide better palliative care. What should they do?