Norm Coleman announced Tuesday that he will undergo surgery later this month to remove part of his lungs after cancer re-emerged there.

“One thing I have learned with the beast that is my cancer is that no single battle wins the war,” the former U.S. senator and St. Paul mayor wrote in a Facebook post that included humor amid the somber update. “With that in mind, my update to you is that the war has not yet been won but it most certainly has not been lost.”

Last August, Coleman learned that the throat and neck cancer he began battling in 2015 had spread to his lungs and was at the most advanced stage. After heavy doses of chemotherapy, Coleman said the tumor was gone.

“There was no signs of cancer,” he wrote.

Still, his doctors had him undergo a program of intensive radiation for five weeks in hopes of crushing the disease.

“But cancer is unrelenting,” Coleman wrote, explaining that a follow-up PET scan showed a spot on his lungs that doctors thought could be either “radiation irritation” or a recurrence of the disease. Another PET scan five weeks later showed the spot had grown and a biopsy determined that the cancer had returned, apparently immune to the focused radiation.

“I’m not intending to give any quarter in this war against the beast,” Coleman wrote, explaining that he’ll undergo a video-assisted thoracoscopic left lower lobectomy, which will remove about a quarter of his lungs and cut his lung capacity by 15 to 20%.

“As I joked with a friend this afternoon, it simply means that if I were to run a marathon that at Mile 20 I would start to get winded,” he wrote. “I will leave the marathons to others.”

Amid the humor, Coleman spoke of gratitude for his doctors, the Mayo Clinic, his family and his friends. But he also gave an unvarnished glimpse of cancer’s toll.

“Cancer sucks,” he wrote. “There’s other words that have been used to demonstrate defiance against the beast of cancer that I can’t repeat here but I know I have used — as have others around me who love and support me every single day.

“There’s the physical toll it takes on the body. The loss of hair. Appetite. Energy. And a host of other indignities that are visited upon most of us who have found ourselves battling in this treacherous war. Yet, for me, it is not so much the physical toll as it is the mental one that I struggle with in the quiet moments of my life.”

By early Tuesday afternoon, his post had generated hundreds of responses and well wishes.

Coleman said he will not let cancer determine how he lives his life. He said he remains active, including traveling the globe for work as well as fishing and spending time at his northern Minnesota cabin. Late last month, he and others escaped injury when his boat was broadsided on Lake Ada.

“I’m hoping the Good Lord didn’t consider that a withdrawal on my good karma account,” Coleman wrote Tuesday of the incident.

As for cancer, Coleman is holding onto optimism. “My war against cancer isn’t won,” he noted. “Yet.”