Andy, 61, of Ipswich, Mass., had a window of good health, a honeymoon of indeterminate time during which he could resume the activities he loved. He played in his coffeehouse band, traveled and took long bike rides up the coast. He also accepted a friend’s invitation to climb in Nepal.
Over three strenuous weeks he and his wife, Jan, who is a registered nurse and an experienced outdoorswoman, trekked alongside eight other climbers and several guides, most of whom they’d traveled with in the past.
In announcing the trip on his Caring Bridge page to ask for donations to fund lung cancer research, Andy had said there was a slim chance he’d summit.
At the altitude he reached, there’s 70 percent less air pressure than at sea level to push air into the lungs. Breathing is hard for the fittest climbers. There was no data on what the high altitude would do to an advanced lung cancer patient: None were found to have tried.
“It’s a remarkable achievement,” Dr. Neilan said. “My colleagues are flabbergasted.”
He gave Andy the O.K. to go to Nepal not as a dying man attempting his last climb but as a person with a deep experience in the mountains who exhibited solid cardiovascular function and health. In the previous months Andy had climbed high peaks in Maine and New Hampshire. Years earlier he’d traveled to Nepal for a trekking trip without incident.
Dr. Neilan, a climber himself, said he found no data around altitude sickness — the most dangerous and common health risk for climbing in high mountains — and Andy’s conditions. But Dr. Neilan knew that at lower altitude even healthy younger climbers tended to have a greater likelihood of pulmonary edema and cerebral edema.
They reviewed a series of warning signs of altitude-related health problems ranging from coughing up blood to severe, unshakable headache. He gave his blessing but acknowledged: “If you polled physicians you might have gotten a lot of different advice.”
Another of Andy’s doctors, Dr. Zofia Piotrowska, a medical oncologist at Massachusetts General, said her team wanted to help him go where he wanted to go, knowing the trip’s meaning to him. However, if she thought the trip was a “medically very unsafe thing to do,” she’d have asked him not to go, she said.
Dr. Piotrowska focuses on the type of lung cancer Andy has, which has a mutation in the gene called epidermal growth factor receptor, or EGFR. The EGFR subgroup represents about 15 percent of all non-small-cell lung cancers and is relatively common in “never smokers” like Andy.
When he was given his diagnosis in 2014, he was treated with a first-generation EGFR inhibitor, an oral pill that turned off the mutant protein on the surface of the cancer cell. His response was swift, but the remission lasted less than a year.
In 2016 he enrolled in his current trial after a biopsy showed his cancer had developed a specific mutation to resist the original drug he’d been on.
A newly developed drug known as EGF816 targeted his acquired resistance.
Within days of being treated, Andy noticed he was breathing better. He resumed his outdoor activities and adventures in the months to follow, doing more as his fitness improved.
Dr. Piotrowska said that before clearing him for the climb, she thought his lung function was pretty close to normal. The question nobody could answer was how lungs that were once filled with cancer would tolerate altitude. Also unanswerable was how he’d respond to the exertion and stress of the expedition, which included waking in darkness in subzero temperatures and a 16-hour climb on summit day.
Andy admitted that he was pleasantly surprised that his doctors signed off.
His most recent scan had confirmed two small, slow-growing nodules, one on each lung. There were no immediate symptoms.
“It’s not like we were told to expect these spots to blossom forth while he was gone,” his wife said. “If we had, it would’ve been an absolute no go.”
A longtime ski mountaineering friend, Brian Lambert, invited Andy to join the trip. They felt he’d be in good hands: the lead guides were Jim Gudjonson, a longtime alpine guide on several of Andy’s previous trips, and Deryl Kelly, an Everest veteran and the head of Parks Canada rescue service who, as an E.M.T., would oversee the clients’ health on the mountain, along with a team physician.
The trip itself was a test. Though Andy went at his own pace the opening week, staying mostly to the rear of the rest of the party as he combined walking steps with periodic “rest steps,” he struggled.
He said he was within a day of letting the others advance on the summit without him when his stamina markedly improved. As they crossed the Mera glacier above 17,000 feet he found himself alongside the group’s faster members. Although it is poorly understood who acclimatizes well and who doesn’t, Andy said he found that he did better at higher altitudes. He likely also benefited from his superb technical skills in using crampons and ice tools on the high glacier.
And he joked that he might have another useful mutation: “I seem to love a sufferfest.”
In ascending on the final day — the climbers were tethered to one another with rope — Andy described the despair of a too-fast pace in the darkness melting in the uplift of a spectacular daybreak. The “beautiful crimson” lit up all the neighboring high peaks, including Everest.
Late last year, he was among several Stage IV cancer patients invited to a small gathering in Boston of top Massachusetts General researchers who outlined their thinking on future therapies. The researchers were clearly energized by the presence of the pioneering patients.
“This is an example,” Dr. Piotrowska said, “of something that none of us ever thought would be possible a few years ago.”
An earlier version of this article mistakenly referred to the therapy Andy Lindsay had as gene therapy. It is targeted therapy, which targets and inhibits the EGFR mutation, but does not alter the patient’s DNA.