The chain will offer 40,000 rooms to patients and caregivers, including half of them for free, over two years. The other half will be available for $12 a night.
The effort is launching in Baltimore and nine other cities, after an initial pilot program in three cities.
The Cancer Society program is called Hope Lodge, and currently offers rooms in Baltimore and around the country. There are 31 locations in the system and accommodations and eligibility requirements vary.
To request a room, call the Cancer Society at 800-227-2345.
Last year, the program provided more than 265,000 nights of free lodging, estimated to cost $38 million.
Traveling for treatment puts a burden on families and caregivers, who are often already emotionally and financially stressed, said Kristen Solt, vice president of the Hope Lodge Network, in a statement.
Extended Stay hopes to continue expanding to every city it serves.