(CNN) Alex Marshall was a freshman in college when she had her first cancer scare.

Intense chest pain and difficulty breathing were serious alarms for the swimmer at Queens University of Charlotte in North Carolina. Her training came to a halt when she ended up in the hospital -- for 10 days.

With the hallmark symptoms of a Hodgkin's lymphoma diagnosis, Marshall and her family feared the worst, but doctors determined that a severe case of mononucleosis was the cause of her problems.

"I was released from the hospital, and I was like, 'OK, we dodged a bullet. It wasn't cancer,' " said Marshall, now 22. The mass in her chest that was causing her pain and other symptoms was covered in the highly contagious Epstein-Barr virus, best known as the cause of mononucleosis.

Two years later, while pursuing a more rigorous academic schedule and training for the Canadian Olympic trials through dual citizenship on her father's side, Marshall began to notice more breathing problems and what seemed like a lingering cold.

"I just played it off, because I was getting cold-like symptoms, and then I would just get over it. And it would come back again two to three weeks later. I dealt with that all of summer."

Come fall, the familiar pain in her chest returned.

Despite the pain and difficulty breathing, her performance in the water did not suffer. Coach Jeff Dugdale saw no signs of health problems in the water but instead was impressed with her performances. "I remember to this day; it was the last weekend of September when we were swimming (at) Auburn. She had one of her best meets where she got her best time."

Still, the complaints prompted Dugdale to send Marshall to the campus wellness center, where staff referred her to a specialist. The days that followed included an X-ray, a MRI and a biopsy of a mass in her chest. Alex had symptoms that suggested Hodgkin's lymphoma, a form of cancer that invades the bodies white blood cells and weakens the immune system.

"Monday rolled around, and I hadn't heard anything, nothing," she said. "I texted my family group chat, 'I haven't heard anything. It's 5 o'clock; we should've heard something by now.' " Her messages were met with encouragement to be patient and that everything would be OK.

But when her parents showed up at her door 30 minutes later, she instantly knew that her test had confirmed their biggest fear: a diagnosis of Hodgkin's lymphoma.

"I didn't hear a word," she said, "it was like the adults in those Charlie Brown movies. Nothing they said made any sense."

In 2015, Alex Marshall took a break from school and swimming to undergo chemotherapy for Hodkin's lymphoma.

'Different than other patients'

According to the National Institutes of Health, most new cases of cancer are found in people over the age of 55, but young adults are more likely than either young children or older adults to be diagnosed with certain cancers , including Hodgkin's lymphoma. And for the adolescent and young adult population, cancer is the leading cause of disease-related death.

Adolescence and young adulthood are already transitional phases that bring unique age-related challenges. Being diagnosed with cancer during this time can be especially trying. The social difficulties faced by this group were highlighted in a study recently published in Cancer, a journal of the American Cancer Society.

The question researchers wanted to answer: Compared with cancer-free peers, how were patients in the adolescent and young adult population affected by a cancer diagnosis?

Over two years, cancer patients ages 14 to 39 self-reported their social functioning.

Researchers found that one in three young cancer patients experienced lower social functioning than their peers. Additionally, although there were improvements in the first year after diagnosis, after two years, social functioning was still worse than that of the general population.

"The cancer diagnosis in this age range is really impactful, not just at the time of diagnosis but through treatment and beyond treatment," said study co-author Dr. Brandon Hayes-Lattin, a professor at Oregon Health and Science University.

Marshall immediately felt the impact of her diagnosis. "Day one, I was really upset," she said. "I was thrown into the spotlight of 'cancer girl,' and I wasn't quite ready for that. I didn't really want that."

I was thrown into the spotlight of 'cancer girl,' and I wasn't quite ready for that. I didn't really want that. Alex Marshall

Her feelings of depression and isolation were similar to those of study patients who reported their lowest scores of social functioning at the time of their diagnosis.

Fueling those emotions and confusion, in part, was the lack of immediate changes to her appearance. "I still had my hair. I didn't really feel different, because when I looked in the mirror, I saw my old self looking back at me, and I still felt great."

That all changed when she began chemotherapy and experienced the common side effects of weight and hair loss. The champion swimmer fought hard to stay in shape and refused to let the drugs deplete her.

"There were two weeks between each session, and once she rebounded, she would do leg lifts or walk around the block," said her mother, Lucia Marshall. "Sometimes, we'd walk around together, and she'd hold on to my arm because she was too weak to stand on her own. She never gave up. Even though she was going through this, she wanted to exercise."

Cancer, Hayes-Lattin notes, can disrupt more than a patient's daily routine. It changes relationships with peers and how a person functions in school and work. Swimming and fitness, for Marshall, occupied a large part of her life and her identity. "Cancer can throw a wrench in that to a substantial degree," Hayes-Lattin said.

"What makes it challenging for adolescent and young adult patients that's different from younger patients and older patients is that there are some really unique things that face this group," said Dr. David Freyer, director of the children's center for cancer and blood diseases at Children's Hospital Los Angeles, one of five institutions involved in the new study. "You think about where they are. They're life planning and in developmental life stages."

Winning in and out of the pool

While she was home, her coaches wanted Marshall to focus on her recovery.

"My promise to her was, 'if we win the national championship and you win your championship, we're going to put "we kicked cancer's ass" inside of our national championship rings,' " Dugdale said.

And they did just that. On March 12, 2016, the Royals men and women's swim teams claimed the NCAA championship for the second consecutive year, and 12 days later -- surrounded by family, friends and teammates -- Marshall completed her final treatment. "The very next day, she was in the water," her mother said.

The next phase and transition, from patient to survivor, presented new challenges.

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"That last day of my chemotherapy treatment, it was really exciting. I rang my victory bell, and I was cancer-free. But I think that's when people kinda cut everything off," Marshall said. " ''You're cancer-free now. You're done with treatment. Go back to your old life.' But that's not the case at all. I had never felt so lost or confused in my entire life. I didn't know who I was anymore."

The struggle with that transition is a sign that "we're not doing the best we can," said Dr. Timothy Griffin, chief of hematology/oncology at the Children's Hospital of San Antonio, another of the institutions involved in the new study.

"You really need to have the care managers, social workers, behavioral medicine specialists, licensed counselors or psychiatrists," he said. "Those people need to be involved in the patient too so they can support the nonmedical part."

Marshall saw therapists both while undergoing treatment and during her transition to life in recovery. She says the assistance really helped during the challenging time.

Marshall tried to find some normalcy and returned to the pool. "I felt like I was gaining (my) identity back more and more each day and less of the cancer girl. It was nice to go back to old activities that I did such as swimming. So that helped navigating my survivorship a bit more in my favor."

In her third appearance competing for a national title, she surpassed expectations with a second-place finish in the 50-yard freestyle, helping the team take home its third consecutive title.

Almost a year after completing treatment, Marshall competed in the Division II NCAA Swimming & Diving Championships. Her team won the national title.

"She gets second place at NCAA," Dugdale said. "She gets her best time, which was pretty amazing considering she didn't have much to lose."

But she did have something to lose. That race was paramount in helping Marshall find normalcy.

Post-cancer, the swimmer is focused on finishing college and chasing another title.

Of course, not everyone needs another championship ring to feel like themselves again. There were other things that helped along the way.

"It sounds super cheesy," Marshall said of what helps her during the toughest moments, "but having my dog helped me through a lot of my struggles. He would always make me feel better."