At 68, John Casterline has beaten advanced-stage lung cancer, prostate cancer and throat cancer. Last month, he finished radiation treatments. Just one week ago, his doctors pronounced him cancer-free. So what is he doing to celebrate?  Forget Disney World. Starting April 28, this Orlando retiree will be hiking 2,650 miles, from Canada to Mexico, along the Pacific Crest Trail — a route that will climb above 13,000 feet elevation and require him to average 20 miles a day. "I expect that I will experience weather that is too cold, too hot, too wet, too dry and too perfect," he wrote in his journal a year ago, when he began training seriously for the hike. "I will encounter rattle snakes, bears, and maybe even mountain lions. … The mosquitoes will be horrendous at times, the hills steep, the rocks sharp, the trail blocked, the wind very strong. [Sleep will be] occasionally fitful and I'll be carrying a backpack with 30-plus pounds." But if you have to ask why he's doing it, he wrote, you wouldn't understand.  It is not simply that he hopes to raise $26,500 for the dramatically underfunded battle against lung cancer, a disease expected to claim the lives of 160,000 Americans this year — more than colon, breast and prostate cancers combined. Nor is it about creating some kind of legacy. Though followers can read his ongoing exploits on lungcancerhike.org, the website is intended to give fellow cancer survivors hope — and to collect donations for the American [...]