By Lucette Lagnado

Ari Bernstein was 22 years old and five months into his first semester at Albert Einstein College of Medicine when he learned he was sick. Sometime last November, he began noticing his neck was sore, and felt a lump at the base of his neck. When he had it checked in December, it turned out to be the tip of a roughly seven centimeter mass wrapped around his heart and trachea.

Doctors wrestled with the diagnosis: Was it a rare cancer that would require major surgery or was it lymphoma, a cancer that was serious but generally responsive to treatment? Or was it a benign mass that still needed to be removed surgically?

The news that he had lymphoma, a cancer of the lymph node system, left Ari torn about whether to stay in medical school or take a leave—as his parents were urging—and return home to Montclair, N.J.

“I had worked so hard and for so many years to get into medical school,” he said. “And now that I was finally here—happy and thriving—my biggest fear was having to take a leave.”

His decision to stay in school comes as many doctors, residents, and medical students are feeling burned out and profoundly frustrated with their work, leading some to quit.

Ari had heard the warnings about physician burnout before applying to medical school. He had been advised to pick another career, such as finance, rather than medicine. But he followed his dream and now that he was in medical school, he wanted to stay the course and become a doctor.

His mom, Risa Bernstein, pushed him to leave school. “I wanted him to come home where I could take care of him, where I could feed him, where I could make him rest,” she explained. Ms. Bernstein had spent years working in health-care communications and co-founded two companies whose clients included makers of several cancer drugs. She worried about the drugs’ toxic side-effects. “I wanted him to focus on healing,” she said. “That was all that mattered to me.”

Ari knew that his physician at Montefiore Einstein Center for Cancer Care, Noah Kornblum, a hematologist-oncologist, could help with the decision. The center is part of the Montefiore Health System. At the initial consultation, Dr. Kornblum spent several hours going over the disease with Ari, his parents and his girlfriend, Dara Levy.

“This kid wanted to be in school,” said Dr. Kornblum, an assistant professor of medicine at Einstein. “He was like, ‘I am not going to let lymphoma [get in between] my meteoric rise in medicine.”

The doctor also managed to reassure Ms. Bernstein. “He held my hand,” she said, recalling him saying, “Ari is going to graduate, he is going to be a doctor and, God willing, he will get married and have children.”

Dr. Kornblum’s supportive stance endeared him to his young patient.

“That was when we had a connection more than [I had] with my parents,” Ari recalled. Montefiore, where Dr. Kornblum practices, is the university hospital for Albert Einstein, which meant Ari could get chemotherapy close to school.

Treatment began almost immediately. As an inpatient at Montefiore in late December, Ari received a drug called Rituxan which is widely used to treat lymphoma, and suffered a severe reaction.

“His body was quaking,” Ms. Bernstein recalled, and he said, “ ‘Mom, I am scared.’ ” She found herself racing through the unit to find a nurse. Her knowledge about the drugs “gave me more fear, because I understood too much about the toxicities even after the treatment stops.”

Ari felt better on New Year’s Eve, which he spent with his girlfriend at his side in his hospital room. They would always remember this night, they told one another gamely over pizza and non-alcoholic cider. Ms. Levy says they chatted “a lot about future New Year’s Eves” and vowed not to spend another one in a hospital.

Ari was back on campus for his second semester a week after leaving the hospital. Chemotherapy caused his hair to fall out and he began wearing a beanie. He became comfortable walking through campus with a portable infusion pump to get the chemo drugs. The pump made a low repetitive whooshing sound during class but his fellow students never complained.

His demanding medical-school workload remained largely the same—except for Anatomy class. Ari was too weak to stand for 2.5 hours each day to dissect cadavers, and he wanted to avoid the formaldehyde due, he said, to his compromised immune system.

Ari said he found support at Einstein for his decision to stick with his training. Mary S. Kelly, a psychologist who serves as director of academic support and counseling, became his liaison, contacting key faculty—including the anatomy professor—to make sure Ari received some dispensation. “Everybody was very sympathetic,” Dr. Kelly says. But they weren’t pushovers. She kept an eye on his grades, to see if he was keeping up, she said. Despite the grueling schedule, Ari says, his grades improved.

To keep up with anatomy, his roommate, Jeffrey Arendash, went to the lab with him every couple of weeks to review the dissections. “I saw the cadavers less than the average person, but I spent more time looking at the textbooks,” Ari said.

Over five months, he had six cycles of chemotherapy, in a center just a two-minute drive from his dormitory. Strong anti-nausea drugs helped but nothing could stave off his exhaustion. Several days after each infusion, he would go home to his parents for a couple of days, then return.

“I didn’t know how hard chemotherapy was going to be,” he acknowledges. His oncologist, Dr. Kornblum urged him to get in touch if he ever suffered a bad reaction. “Call me even if it is the middle of the night,” the doctor said.

When he did well in class, Ari texted him; Dr. Kornblum, he believed, savored hearing such news.

One day in pharmacology class, his professor gave a presentation about cancer drugs. Ari realized he had been on most of them: “I knew these drugs probably better than the professor,” he said. “They were inside of me.”

When he took exams, special arrangements had to be made. Given his weak immune system, he couldn’t be in a room with scores of other students. Instead, he took tests alone with Dr. Kelly as his proctor.

In June, Ari had another test—a scan. Dr. Kornblum declared him to be in “complete remission.”

Looking back, Ari thinks that his illness, along with his bond with his oncologist, has changed his perspective on medicine. He has become more interested in urology, a field that would allow him to treat cancer patients, and can foster close doctor-patient relationships. This past summer, he addressed a pediatric urology conference in Montreal on some research. He sent his doctor a photo of himself on stage. “One of many to come,” Dr. Kornblum replied.