The press release published by the company said Luc Oursel recently told the French government he was going to take a leave to to pursue treatment.
State-controlled Areva, which is controlled by the French government, is struggling through a complicated turnaround due to France's plans to move away from nuclear energy after the earthquake and tsunami at the Fukushima power plant in 2011.
Oursel has led investments in renewable energy, but the sector still makes up a small part of Areva's business.
Luc Oursel said:
"Under these very difficult personal circumstances, and despite my very strong commitment to AREVA, I have had no choice but to hand over my responsibilities at the head of the company and have chosen to take a leave of absence in order to pursue treatment. I must now fight a personal battle against the illness, but all of my thoughts remain with the teams at AREVA. I have been happy and proud to mobilize them in the difficult context for the turnaround of the company, for the benefit of the country, and I am convinced that they will succeed."