Cancer patient Tom Galjour does an oxygen treatment at his apartment in Houma, Louisiana, U.S., on Tuesday, Feb. 3, 2015. Almost three years ago, Galjour was diagnosed with Stage 4 metastatic small-cell lung cancer exacerbated by emphysema. The lung tumor that had very nearly killed him has not only shrunk under a bombardment of radiation and chemotherapy, it has been rendered 'metabolically inactive,' which means essentially dead. Galjour's experience to date puts him among what oncologists call 'exceptional responders,' patients who because of some combination of genetic makeup and will react favorably to conventional or experimental medicines and treatments and beat the odds on cancers that defeat most people. Photographer: Luke Sharrett/Bloomberg via Getty Images