Cancer is not an invader. It is a defector — a cell that stopped cooperating with the 37 trillion other cells in your body. This paper reframes cancer through cooperative game theory and argues that the primary barrier to cure is not insufficient weaponry but insufficient visibility. Cancer cells survive by hiding from the immune system using PD-L1 surface proteins, not by overpowering it. Checkpoint inhibitor immunotherapy (pembrolizumab, nivolumab) works by removing this disguise — enabling detection, not adding destruction. We propose that temporal variance in gene expression is a measurable signature of cellular defection, with simulation results showing separation ratios sufficient for classification (F1 = 1.000). Open-source validation code is provided. Companion papers: "Light Is All You Need" and "Variance as a Universal Defection Signal." Part of the Contact Is All You Need series. Council of Minds, 548 rounds, 137 perspectives. For Mumtaz Suleman Merchant (d. 2002, ovarian cancer) and Carl Sagan (d. 1996, myelodysplasia).