Veronesi, 88, made the comments in his new autobiographical book, The Craft of Man (Il mestiere di uomo).
“I have come across something more unexplainable than war: cancer,” he was quoted in Il Messaggero as saying.
“After Auschwitz, cancer is further proof that God does not exist,” said Veronesi, who was called up to join the Italian army in the 1940s.
Despite growing up in a strongly Catholic country, Veronesi said his work could not be reconciled with religion.
“My choice to become a doctor is fundamentally tied to original research,” he said, which clashes with “the concept that God cannot be explained”.
“I couldn’t tell you which was my first day without God. Certainly, after the experience of war, I no longer stepped into a church, but the decline in trust started long before,” said Veronesi, describing the “Catholic doctrine” he experienced at school.
Veronesi recently stepped down as scientific director of the European Institute of Oncology (IEO), but continues to play a role in Italian health issues.
Last year, he weighed into the debate on e-cigarettes, calling on the government to change their approach to the controversial new product. Tobacco-free cigarettes could save 30,000 lives in Italy a year, Veronesi said, and should be seen as a chance to improve public health.