Maura Tierney

When Maura Tierney returns in the final season of Rescue Me, her character will be battling cancer, the disease Tierney was recently treated for in real life, the show's co-creator tells TVGuide.com.

See photos of Tierney through her career

After Tierney received a clean bill of health, Rescue Me co-creators and executive producers Denis Leary and Peter Tolan approached the 45-year-old actress about portraying her character, Kelly McPhee, in the middle of receiving cancer treatment. After some thought, she agreed, Tolan says.

Tolan says Tierney, who will appear with what he calls a "buzz cut," even helped fine-tune the story.

"We wrote like dopes. We haven't had cancer, and we wrote stuff that was a touch melodramatic perhaps," Tolan says. "She got me on the phone one time, and we had the most fascinating conversation. She tried to explain to me what it felt like and what was going through her mind. ... It actually took me a long time to figure out what she was saying."

Exclusive: Maura Tierney will be back on Rescue Me

McPhee was first introduced in the FX drama's fifth season. She memorably ran into a burning building to retrieve an important box and later bonded with Tommy (Leary) because both of them had lost children. Kelly's cancer allows for a different kind of bond with Tommy this time around, Tolan says.

"It's about survival and anger — it is anger at survival," Tolan says of the new story line. "That was one of the things that Maura said. Even though she got a clean bill of health, her initial response was not relief. It was anger and, 'Why did I have to go through that?' And that fits right into Tommy's, 'Why did I have to experience what I've experienced? Wouldn't it have been easier to just die than to go forward in fear?'

"I don't think Maura feels like she's got anything hanging over her head, but Tommy does, and that may be the difference between the two of them," Tolan says.

Tierney had a tumor removed from her breast in 2009, and dropped out of NBC's Parenthood to continue treatment. She has since appeared in New York and Los Angeles productions of the play North Atlantic, and will star as a lawyer in ABC's new legal drama The Whole Truth.

Tierney's rep did not immediately respond to a request for comment, but Tolan applauds Tierney's bravery. "[Maura] got well and then went back and played someone who was sick," he says. "She relived her illness for the show and the character. That's balls, right there."

Rescue Me's Season 6 finale airs Tuesday at 10/9c. The seventh and final season will begin in 2011.