For 36 years, Donna Fernandez was a smoker.

"I probably started smoking when I was 17," she said, adding she smoked at least one pack of cigarettes a day during her time as a smoker.

"It was like I was missing something that cigarettes fulfilled," she said.

After she quit, her doctor found a small lump near her collarbone that turned out to be a tumor. She was diagnosed with Stage 4 lung cancer.

"Immediately, I flashed back to my dad," she said.

Her father was diagnosed with the same type of cancer in the 1970s — and died six months later.

"I'd always said, I'll do radiation but I'll never do chemo because that made him so sick," she recalled.

Her aggressive cancer meant Fernandez wasn't a candidate for surgery or radiation. She tried chemotherapy, which only worked temporarily.

"At that point I felt like I was probably here for a limited time," said Fernandez.

She is now taking part in an Immunotherapy clinical trial at UT Southwestern.

"With immunotherapy, we're seeing in a minority of patients, very long-term survival," said Oncologist Dr. David Gerber, who specializes in lung cancer.

The idea behind immunotherapy is to kickstart the body's natural immune response to a cancer.

"Not only does immunotherapy appear more effective than chemotherapy in lung cancer, but it's better tolerated," said Dr. Gerber.  

While patients may experience some side-effects due to immunotherapy, they've been minimal for Fernandez. Largely, she's been able to continue to enjoy her life three years after her diagnosis — which means her stage 4 lung cancer is being controlled.

"That's pretty unusual," said Dr. Gerber. "Historically, when we think about stage 4 lung cancer, the average survival is about a year."

Fernandez now spends much of her free time with her husband of 41 years, and with her dogs, Barney and Cotton. She even trains them to do obstacle races.

"I finally found something I love more than smoking -- and that was doing agility with my dogs," she said.

Fernandez is hoping immunotherapy will give her many more good years.

"I hope I can do it until I'm 90!," she said.