The actress shared an uplifting "Peanuts" cartoon to her Instagram page on Tuesday morning, but didn't explicitly address her condition.
In the illustration, Charlie Brown appears to be sitting on a dock next to Snoopy.
"We only live once, snoopy," Charlie Brown says.
"Wrong! we only die once. We live every day!" Snoopy replies.
The post generated an outpouring of support from fans.
"You have always been one of my favorite actresses and Brenda Walsh is my favorite tv character ever !" one person wrote. "I always looked up to you when I was growing up . I am so very sorry that you are going through this again . Sending prayers and positive thoughts your way !!"
Doherty most recently appeared on the “90210” reboot last summer.
In 2019, she talked about how her life had changed after surviving her first bout with cancer.
"I really took good care of myself, and I came out of it in as good of condition I think somebody (in my situation) could be in," she told People.
"But the funny thing with cancer is that once you’re no longer on chemo or radiation, people think you’re fine, that you bounce back. But what they don’t realize is that your body has been through something so incredibly difficult that your body never fully bounces back."
"I don’t think about the fact that I’m in remission," she added. "I look at it like I’m lucky to be alive every minute, every second of the day."