A few years ago, a nephew of mine died of an opiate overdose. Yes, my sister, whose son he was, grieved deeply. And she didn't talk with me for many months after I told her that her grief, of course, was selfish. She felt sorry for herself, not for her son.
From all we know about death from an overdose of opiates, he had a good death. Unintended, free of pain. Opiate overdoses are deadly because they suppress the respiratory center of the medulla in the brainstem. Basically, a person just forgets to breathe, and feels no panic about this.
A rather famous German journalist with whom I covered Southeast Asia in the early 1980s died of cancer not long ago. The magazine he worked for wrote that after he received the diagnosis, he retreated to a Himalayan hideout where he awaited death untreated, just meditating, leaving his family behind in Germany.
I don't know whether the details are true or not. But I know that many cancers are very painful.
If I were diagnosed with cancer, I would probably also prefer to await my end somewhere in the Himalayas. At least that is a part of the world that is still very lenient about the use of opiates.
Maybe meditation, as well as medication, can help relieve cancer pain. But not if you start meditating after being diagnosed with cancer. For meditation to work in lieu of pain medications, one would probably need a lifetime of meditation practice, and the biological effect against cancer pain would still depend on morphine—or more precisely, in this case, endorphins, substances produced by the body that are chemically almost identical to morphine.