The figure was based on how long it took two recent cancer drugs to be approved across the world after they were given the green light by the United States.
Pembrolizumab, which treats most lung cancers, was approved by the US Food and Drug Administration (FDA) in 2016.
More than 600,000 years of patients' lives could have been saved if Brazil, Canada, China, India, Japan and the European Union had approved the drug at the same time, according to an analysis published in the Harvard Business Review, which is not peer-reviewed.
The authors, including US oncologist Bobby Daly, also looked at enzalutamide, which is used to treat prostate cancer.
Enzalutamide was approved by the FDA in 2012, and the analysis by the Bloomberg New Economy International Cancer Coalition found that 284,000 years of patient lives could have been saved if other countries had approved the drug alongside the FDA.
Researchers estimated that if each of the approximately seven cancer drugs approved by the FDA a year were authorized worldwide, it would reduce the number of cancer-related deaths by 10-20 percent.
That represents roughly 1.5 million of the around 10 million people killed by cancer every year.
The study assumed that the rest of the world had the infrastructure to diagnose and treat cancer as well as the US, which is not always the case.
The authors of the analysis called on countries to embrace Project Orbis, a US-led framework aiming to get cancer drugs trialed and approved at the same time in multiple countries.