The bassist has played and performed backing vocals with the rock band since their formation in 1991.
The band recently got back together for a reunion tour this summer, with Commerford announcing in a new interview that he had had his prostate removed two months before the shows kicked off in July.
Only his family, bandmates and a close group of friends were aware of his diagnosis.
“I’ve been dealing with some pretty serious s***,” Commerford told Spin. “Right before I was about to go on tour with Rage, I had my prostate removed, and I have prostate cancer.”
Commerford said that he had always taken care of his health, but the cancer was simply “something where either you’re either lucky or not”.
“You can find yourself in a situation like I’m in where it’s like, f***, my whole life changed,” Commerford said. “With everything that happens to me now, I wonder, am I feeling this way because I have cancer? Am I losing my hair because I have cancer? Whatever it is, it makes me wonder if it’s happening because I have cancer.”
The 54-year-old said that because the prostate was “connected to your sexuality”, he found the subject particularly “hard to talk about”.
“It’s a brutal psychological journey… The suffering part of it, the physical suffering after the surgery, I’ve never felt pain quite like that… I’ve always felt like I had a really high tolerance for pain, and that s*** brought me to my knees,” he explained.
“After the pain went away, I still haven’t really been able to get up, even though I’m working out and doing s***, but psychologically, the damage is severe. It’s very hard for me to not break down and get emotional.”
Commerford said that his health warning had come when he’d struggled to get medical insurance due to irregular PSA (prostate-specific antigen) levels.
“I watched it over the course of a year and a half, and it kept elevating further. Eventually, they did a biopsy and found out I had cancer, so they took my prostate out,” he said. “I blame myself. I should have said, ‘My numbers are elevated and what does that really mean?’ I should have taken it more seriously.
“Now I’m in the situation that I’m in, which is, hold your breath for six months. It’s not a good one and not one that I’m happy about. I’m just trying to grab ahold of the reins. It’s gonna be a long journey, I hope.”