Dr. Bryant Lin stood before his class at Stanford in September, likely one of the last he would ever teach.

Just 50 years old and a nonsmoker, he had been diagnosed with Stage 4 lung cancer four months earlier. The illness is terminal, and Dr. Lin estimated that he had roughly two years left before the drug he was taking stopped working. Instead of pulling back from work, he chose to spend the fall quarter teaching a course about his own illness.

Registration for the class had filled up almost immediately. Now the room was overflowing, with some students forced to sit on the floor and others turned away entirely.

“It’s quite an honor for me, honestly,” Dr. Lin said, his voice catching. “The fact that you would want to sign up for my class.”

He told his students he wanted to begin with a story that explained why he chose to pursue medicine. He picked up a letter he had received years earlier from a patient dying of chronic kidney disease. The man and his family had made the decision to withdraw from dialysis, knowing he would soon die.

Dr. Lin adjusted his glasses and read, choking up again.

“‘I wanted to thank you so much for taking such good care of me in my old age,’” he read, quoting his patient. “‘You treated me as you would treat your own father.’”

Dr. Lin said this final act of gratitude had left a lasting impact on him. He explained that he had created this 10-week medical school course — “From Diagnosis to Dialogue: A Doctor’s Real-Time Battle With Cancer” — with similar intentions.

“This class is part of my letter, part of what I’m doing to give back to my community as I go through this,” he said.

Later, an 18-year-old freshman in his first week at Stanford caught up on a recording of the class, which was also open to students outside the medical school. The course had filled up before he could enroll, but after emailing Dr. Lin, he received permission to follow along online. He had questions that needed answers.

From Doctor to Patient

Last spring, Dr. Lin developed a persistent and increasingly severe cough. A CT scan showed a large mass in his lungs, and a bronchoscopy confirmed the diagnosis: cancer. It had metastasized to his liver, his bones and his brain, which alone had 50 cancerous growths. He is married, with two teenage sons.

The diagnosis was particularly cruel given his work. Dr. Lin, a clinical professor and primary care physician, was a founder of the Stanford Center for Asian Health Research and Education. One of its priorities has been nonsmoker lung cancer, a disease that disproportionately affects Asian populations.

A self-described “jolly” person, Dr. Lin is known for his booming laugh and voice made for radio. A longtime mentor called him a “pied piper” for ideas — someone who can rally people around a vision. In addition to his other work, he directs the medical humanities program at Stanford and has patented medical devices.

Across his roles, he stresses that people are at the heart of medical practice. He said he tries to emulate an “old-timey country doctor” and once helped throw a 100th birthday party for one of his patients.

Dr. Lin learned that his cancer was advancing rapidly. He felt pain in his spine and ribs, and his weight dropped. His doctor put him on a targeted therapy designed to attack the specific mutation driving his cancer. He also underwent chemotherapy, which caused nausea and sores in his mouth.

“Day in the life of a cancer patient,” he said in a video diary he began keeping after his diagnosis. “So I guess that’s what I’ve become. Rather than a dad or husband.”

After a few cycles of chemotherapy, his breathing and coughing began to improve, and scans showed drastic reductions in the cancer’s extent. He continued to see patients and teach, and he began to think about what to do with the time he had left.

The dying dialysis patient had written a letter because he wanted Dr. Lin to know he was appreciated. Dr. Lin had a couple of ambitions for his own message to his students. He liked to think that some of them, having taken his course, might go on to dedicate themselves to some aspect of cancer care. And he wanted them all to understand the humanity at the core of medicine.

The ‘Primary Care’ Model

Dr. Lin’s class met for about an hour each Wednesday. One week, he led a session on having difficult conversations, where he stressed that doctors should be honest enough to say “I don’t know” when necessary — an answer he had to accept as a patient amid the uncertainties of his own diagnosis.

In another class, he discussed how spirituality and religion help some patients cope with cancer. Though he isn’t religious, he shared that he found comfort in others’ offering to pray, chant or light a candle on his behalf.

And in a session on the psychological impact of cancer, Dr. Lin spoke about the disappointment he felt after a scan showed that some of his tumors had shrunk but hadn’t disappeared — because, deep down, he was still holding out hope for a miracle.

He taught the sessions using what he described as the “primary care” model. He was the initial point of contact, sharing how his cancer diagnosis had affected him, but he referred his students to specialists — guest speakers — when more exploration was needed.

One of his first guests was Dr. Natalie Lui, a thoracic surgeon and lung cancer expert. Standing before a set of slides, she placed Dr. Lin’s diagnosis within the broader context of lung cancer among nonsmokers, particularly in Asian populations.

“In the U.S., about 20 percent of people diagnosed with lung cancer never smoked,” she said. “But in Asian populations and Asian American populations, that could be really up to 80 percent in some racial and ethnic groups,” she added, with Chinese women especially likely to receive the diagnosis.

For a class on caregiving, Dr. Lin brought in Christine Chan, whom he introduced as “my wonderful wife.” The students, some in scrubs, had been chatting and laughing, but grew quiet as the session began. Chairs shifted closer, and one person stood to get a better view.

Like her husband, Ms. Chan softened difficult truths with a smile, meeting students’ eyes across the audience. She spoke to the students as though they were or would become caregivers themselves.

Ms. Chan said she had been overwhelmed at first, buried in medical terminology she didn’t understand. Wanting to give her husband the best chance at continued health, she tried cutting out sausages and red meat from his diet — but felt disappointed when he turned down some of the new foods she made. While she encouraged caregivers to lean on friends and family, she warned that coordinating well-meaning offers of help could become a task in itself.

An M.I.T. graduate and program manager at Google DeepMind, she acknowledged that letting go of her instinct to plan for the future had been difficult.

“We just have to go through it one day at a time,” she said. Dr. Lin nodded in agreement.

A Job Not Quite Finished

Watching Dr. Lin teach, I often wondered what his students, many in their late teens and early 20s, were thinking. What was it like for them to become attached to him as a professor, knowing his prognosis was so dire?

When I asked, some used the phrase “once-in-a-lifetime opportunity” to describe the course. Others saw Dr. Lin as brave and said that if they were in his position, they probably wouldn’t be teaching a class.

But a significant number of students said they were confused. They had signed up for the course expecting something more “existential,” as one student put it. They were prepared for a harrowing emotional experience. But, save for choking up during the first lecture, Dr. Lin remained steadfastly upbeat, even cracking jokes.

When his wife told the class about cleaning up his diet, he feigned alarm, saying, “I’m like, ‘I don’t eat this food!’” And when he quizzed his oncologist, another guest speaker, about what might come next for people who developed resistance to the drug he was taking, Dr. Lin quipped, “Asking for a friend!”

It was difficult for some students to reconcile this upbeat attitude with the severity of his diagnosis. Gideon Witchel, of Austin, Texas, was one. He was the 18-year-old freshman who had watched a recording of the first class from his dorm room. A spot had since opened up, and now he was enrolled.

When Mr. Witchel was 5 years old and his sister was 3, his mother, Danielle Witchel, was diagnosed with breast cancer, but he had never talked to her about it in depth. He had never been able to say, “Tell me the story of your cancer.” He was taking Dr. Lin’s class in hopes that it would help him start that conversation.

One of his strongest memories of his mother’s illness was of playing with her colorful scarves while she sat on the couch, bald. But looking back, he felt unsettled. The thought that she could have died was terrifying.

During the session on spirituality, the idea of control came up, and that gave Mr. Witchel the opening he needed to approach Dr. Lin. He lingered after class and asked the professor whether he had chosen to teach the class to regain a sense of control over his diagnosis.

Dr. Lin replied without hesitation: no. He said he tried not to dwell on what was out of his control. “I’m very conscious that I have limited time left,” he said. “So I think about that. How am I going to live my life today? Is this a worthwhile way to spend my time?”

The class, he said, was worthwhile. “Does that make sense?”

“It’s powerful,” Mr. Witchel said. “It’s impressive that you’re doing this.”

“You know, I think if I were 20, it would be different,” Dr. Lin responded. He said his work as a doctor had perhaps enabled him to cope faster than other people would. He asked again, “Does that make sense?”

Mr. Witchel nodded, and Dr. Lin smiled, this time with a shrug.

Sometimes, in private, Dr. Lin was less sanguine than he appeared in class. More than once, he told me, he looked back on time passing and thought, “Wow, that was a fast week.”

When he saw an older person, he was reminded that he probably wouldn’t live to be that age. What hurt was missing not the opportunity to grow old, but what growing older represented — the chance to attend his children’s graduations, to watch them grow up and start their own families. The expectation of spending his later years with his wife.

Dr. Lin and Ms. Chan had told their children about his diagnosis, but they weren’t sure the boys fully understood what it meant. It was hard to think of a man as dying when he looked as healthy as Dr. Lin did. “They think, Daddy can take care of everything, fix everything, solve everything,” Dr. Lin said.

He referred to the class as his letter to his students, but he had crafted an actual letter to his sons for them to read after he was gone.

“Whether I’m here or not, what I want you to know is that I love you,” he wrote. “Of the many things I’ve done that have given my life meaning, being your daddy is the greatest of all.”

The ‘Luckiest Man’

For the last class, held on a sunny day in December, Dr. Lin and his students met in a library at Stanford Hospital. The room was walled in with glass, offering a view of the foothills and flowering plants on the adjoining rooftop garden. Students spilled over from the designated seats into a computer cluster, and the librarian leaned against one of the sections of shelves to watch.

Near the end of the class, Dr. Lin stood at the front of the room, folding and unfolding a piece of paper where he had printed his closing remarks. It was time to finish his letter.

He gave what he called his version of Lou Gehrig’s farewell speech, referring to the Hall of Fame baseball player for the New York Yankees who died at 37 from amyotrophic lateral sclerosis, or A.L.S., an incurable neurological disease.

Dr. Lin unfolded the paper once more, this time all the way.

“For the past quarter, you’ve been hearing about the bad break I got,” he said, echoing parts of Gehrig’s address at Yankee Stadium. “Yet today, I consider myself the luckiest man on the face of this earth.”

With that, he choked up. “Sure, I’m lucky,” he said. He said he was lucky to have his two sons, who brought joy and laughter into his house. His teaching assistants, who made the course possible. The Stanford community, his colleagues and the people at the Asian health center. His students and residents. His patients. His friends. His parents. His wife.

“So I close in saying that I may have had a tough break, but I have an awful lot to live for,” he said. “Thank you. And it’s been an honor.”

It seemed clear that Dr. Lin had achieved at least some of his goals. When he asked whether students were thinking of careers in cancer care, about a third raised their hands. The ones planning to be doctors told me they would remember Dr. Lin’s story when seeking to understand their patients’ experience of illness.

But the class moved students in ways he hadn’t anticipated. I talked to several students who said they had advised their parents to get screened for lung cancer. A master’s student told me they were integrating vocabulary about lung cancer into the Mandarin class for medical trainees that they planned to help teach in the winter.

For Mr. Witchel, the effect of the quarter was more personal. He had finally talked to his mother about her cancer.

He told me his story as we sat at a table outside Tresidder Memorial Union, a student center in the heart of campus. His mother had come to visit him during the fall, and he had told her about Dr. Lin’s class and broached the subject with her. The class had removed the taboo from his thinking, and he was able to start talking without the discomfort he had once expected to feel.

He learned that she had something in common with Dr. Lin: letters.

During her illness, Ms. Witchel had written messages to family members and friends. Some wrestled with her uncertainty about whether she would survive, as well as the effect her diagnosis might have on her children. They became a way for her to process what she was experiencing and to connect with loved ones.

“There has been a shuttling back and forth between a very private experience and a very public experience and both have given me strength,” she wrote in one.

After she went into remission, she compiled the writings along with medical records, photographs and other documents into a book bound with ribbon. When Mr. Witchel returned home for Thanksgiving break, he sat down at the kitchen table with the book and his parents, his mother tucked between him and his father.

Together, they alternated between reading from the book and talking. They laughed and cried. For the first time, Mr. Witchel felt he was interacting with his mother as an adult.

In her letters, he heard echoes of Dr. Lin’s philosophy. In one passage, she wrote about the puzzles scattered throughout the waiting areas in the hospital where she received care. Difficult puzzles with hundreds of pieces that “no one person could possibly finish no matter how long the wait.”

Perhaps that was the point, she wrote. Not to finish, but to try.

Audio produced by Sarah Diamond.