(CNN) -- The hike to the bottom of the Grand Canyon -- and out again -- was symbolic for Melissa Schaaf. It was a sign of how far she had come, a sign that the middle-aged mom of two was active, adventurous and alive.
She had lost 80 pounds over the last year and a half through regular exercise and a healthy diet. She was in the best shape of her life, and the trip to Arizona's natural wonder was a chance to celebrate.
It was a grueling hike, about 15 miles down and up the steep trail with hundreds of switchbacks.
But on that day in summer 2011, Schaaf had no idea her biggest battle was yet to come.
Four years ago, the 5-foot-4 Schaaf weighed close to 250 pounds. "When I turned 40, I looked down at the scale and thought, 'Oh my, I must really do something about this,' " the Herndon, Virginia, woman says.
A friend convinced her to join a local Sport & Health Club, and the pair started attending group fitness classes. Schaaf liked spinning, which allowed her to burn calories without pounding her joints with the extra weight she was carrying. Step aerobics was another story -- "I'm jigging when everyone was jogging" -- but being able to laugh at her lack of coordination kept Schaaf coming back.
After a while going to the gym became just another habit, like brushing her teeth.
"I used to be very emotionally vested in hating the gym," she says. "You're not emotional about brushing your teeth. It's something I do because I want to have teeth when I'm old. I want to be able to move when I'm old."
The first 50 pounds seemed to fall off Schaaf. After eight months, she joined Weight Watchers to overhaul her diet. In the past she had tried everything from hypnosis to prepackaged meals to restriction diets to lose weight. But eating better wasn't such a big deal after conquering the gym.
"I'm the kind of person where I can change one habit ... at a time," she says. "I found that trying to master everything at once was just too much."
Schaaf hit the gym five to six days a week and traded cookies for apples and bananas on her kitchen counter. Within a year she had lost another 30 pounds. The aches and pains that had come with her extra weight and advancing age stopped. She felt confident and more at ease. She looked forward to living a longer, happier life.
In December 2011, Schaaf had an elective hysterectomy. During surgery, her doctor uncovered a tumor in her uterine muscle and removed it for testing. The tumor was leiomyosarcoma, a rare cancer that's often only discovered in the terminal stage.
Schaaf's cancer was stage I.
She started the first of four rounds of chemotherapy in February 2012. Through it all, she continued to hit the gym and make healthy food choices. At the gym, her goal was simply to keep moving. And if ice cream was all her stomach could handle, she chose frozen yogurt.
"So much of what's happening to you is out of your control," she says. "I wanted to control what I could."
Overall health during cancer therapy is critical, says Schaaf's oncologist, Dr. Amy Irwin. "We encourage (patients) to eat healthful meals, exercise and continue in activities they enjoy."
Exercise helped Schaaf sleep better at night and work through some of the drugs' side effects, such as constipation and nausea. She went to the gym the morning of her chemo treatments to relieve stress. "It helped me mentally -- kept me strong, kept me balanced."
Patients should stay involved in life, Irwin says, to avoid obsessing about their cancer diagnosis. "Given the supportive medicines we have, most patients are able to maintain normalcy."
Schaaf's weight loss may have done more than prepare her mentally for the challenge ahead. Obesity has been linked to cancer incidence rates. And research has shown that cancer patients who are overweight have a higher risk of mortality than patients with a normal body mass index, Irwin says.
Schaaf is now in remission and has kept the weight off for more than three years. She still has about 10 pounds to lose to reach her goal weight, but she's says she's not in any hurry.
"It think it's all about being patient and ... making the best choices every day," she says. "Do I make great choices every day? No. But you've got to be forgiving with yourself and wake up the next morning and say, 'Today, I'm going to do better.' "
Her healthy lifestyle has increased her energy and opened her eyes to new opportunities. She plans to run a half marathon at the end of April with a bunch of her girlfriends from the gym, and hopes eventually to tackle the Grand Canyon again.
"Hopefully it's not once in a lifetime," she says of her first symbolic hike. "There (are) no limitations anymore."