Are cancer deaths always painful?

No. Cancer pain usually results from spread to bone or nerve, sometimes local measures can keep these under control. Some cancer deaths are agonizing and require a great deal of medication. Others are pain-free, as was my late mother's. In contrast to the barbaric policies of the past, today's politicians are more willing to allow physicians to manage end-stage cancer pain.
No. Some cancers, especially in the central nervous system (brain) can produce chemicals which cause a general feeling of euphoria. Even painful cancers (like bone) can be relieved by appropriate use of opioid pain medication and with hospice care. Dr. J.