Follow the ups and downs in the search for a cure and see promising immunotherapy treatments.

This episode starts at a moment of optimism: Scientists believe they have cracked the mystery of the malignant cell, and the first targeted therapies have been developed. But very quickly cancer reveals new layers of complexity and a formidable array of defenses. Many call for a new focus on prevention and early detection as the most promising fronts in the war on cancer. By the second decade of the 2000s, the bewildering complexity of the cancer cell yields to a more ordered picture, revealing new vulnerabilities and avenues of attack. Perhaps most exciting is the prospect of harnessing the human immune system to defeat cancer. A 60-year-old NASCAR mechanic with melanoma and a six-year-old with leukemia are pioneers in new immunotherapy treatments, which the documentary follows as their stories unfold.