My mom struggled with lung cancer for two terrible years with cutting edge treatment, and died badly. My dad cared for her through that, and when his turn came five years later, he had no doubts. He refused all but palliative care and died in two months. What he saw once, a physician will see over and over ad nauseam. Having seen one of each, I'm not conflicted over which path I'd take.
edit: for the remarkably special downvoters (stay classy HN) - that's the type of lung cancer my mother died from, in about 20 months time. You generally can't surgically remove small cell lung cancer. It was particularly brutal, with endless treatment attempts that were physically grueling and minimally effective. It's a highly aggressive cancer with a very low survival rate and few good treatment options. Accordingly, having watched her go through that, I can very much relate to what the parent said.