Chelsea women's keeper Berger diagnosed with recurrence of thyroid cancer
Berger was first diagnosed in 2017, when she made a full recovery within four months.
"I am working closely with my club doctor and specialist in London and my treatment will start this week," Berger said in a statement.
"I remain positive that my treatment will be as effective as last time and I'm looking forward to returning to the pitch and seeing you all at Kingsmeadow and Stamford Bridge."
Berger was a member of the Chelsea squad that won the last three Women's Super League titles. She was also in the Germany squad that finished as runners-up at last month's European Championship.
"Everyone at Chelsea is behind her during this difficult time and the club will provide any support we can to help her make a speedy recovery," the club said.
"We look forward to seeing her back between the posts for the Blues as soon as possible."