A yearlong international investigation into one of the world's most important cancer drugs shows how a medical breakthrough has also become a fault line in global health, exposing how pricing systems, patent protections and regulatory frameworks determine who can access life-saving treatment and who cannot .

The Cancer Calculus , coordinated by the International Consortium of Investigative Journalists (ICIJ) with Deutsche Welle and 46 media partners, brought together 124 journalists in 37 countries. Drawing on hundreds of interviews with oncologists, patients and their families, lawyers, regulators, pharmacists, pharmaceutical industry insiders and others as well as exclusive pricing data and patent analyses, the project examines how Merck's cancer drug Keytruda became both a therapeutic milestone and a symbol of unequal access.…