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Dr. Daniel Geynisman felt as if he had abandoned his patient, a sickening sensation.

A 65-year-old man with metastasized gall bladder cancer had developed intractable pain before the doctor went away on vacation. By the time Dr. Geynisman returned, the patient was enrolled in hospice; he died soon thereafter. The oncologist never saw him again.

The sudden termination of a close doctor-patient relationship is a common, wrenching scenario. “I can tell you, it happens all the time and it breaks the heart of patients and families and oncologists,” said Dr. Diane Meier, director of the Center to Advance Palliative Care at Mount Sinai’s Icahn School of Medicine in New York City.

In an article published recently in the Journal of Clinical Oncology, Dr. Geynisman described his own experience with this sort of estrangement. He referred to his patient as “MM,” but the man’s actual name was Paul Rieger. He was a math teacher in the Chicago Public Schools who loved to golf and fish and who was married to his college sweetheart. Dr. Geynisman saw the couple every two or three weeks — and sometimes more often — during the last year of Mr. Rieger’s illness.

In a phone interview, the doctor described his patient as “very accepting, very calm, very kind, a gentle soul.”

From the beginning, the Riegers made clear what they wanted from their physician. “I distinctly remember during our first meeting they said they were looking for someone who would be with them through the end, throughout the whole journey,” Dr. Geynisman said.

Yet it was routine for oncologists at University of Chicago Medicine, where the doctor was then working, to stop seeing patients when treatment ended. “The model was, you get to know the patient and their family, you treat them aggressively, but when the time comes that you don’t have any more therapy to offer, you make a referral to palliative care or hospice and the patient goes under their auspices,” Dr. Geynisman said.

Dr. Otis Brawley, chief medical officer of the American Cancer Society and professor of oncology at Emory University, offered another reason oncologists sometimes disappear from their patients’ lives in these circumstances. “It’s a way of protecting yourself from the devastating feeling that you’re letting this person down and your inability to keep them alive is a professional failing,” he said.

That isn’t to say it’s justified. “No physician should ever say there’s nothing more I can do,” said Dr. Timothy Moynihan, medical director of the Mayo Clinic hospice, who wrote a response to Dr. Geynisman’s article noting that oncologists can remain involved with patients in hospice as the physician of record. “There’s always something more we can do for the patient — if only to be there and listen to their stories and deal with their pain and suffering.”

Dr. Geynisman said he had never received training about how to interact with a patient whom he could no longer help. But he felt terrible about not calling Mr. Rieger before his death and vowed this would never happen again.

“Do patients and their families want me, the primary oncology physician, to be around for the last phase of their lives?” he wrote in his article, which inspired dozens of emails from fellow oncologists across the country. “Do I ultimately break my pledge to patients as I prematurely end my journey with them when there is no longer ‘active therapy’ to offer them?”

The answer is yes, suggested Dr. Meier of Mount Sinai.

“Very often, one of the major sources of emotional and spiritual suffering among patients who are nearing the end of life or a prolonged illness is the abandonment they feel when they stop being cared for by a physician to whom they have become attached,” she said.

Dr. Meier told the story of a New York City oncologist who gave “impeccable” care to a woman with lung cancer, keeping her alive for almost seven years. Dr. Meier began caring for the patient as well when the oncologist turned away from addressing her questions about death. (“What exactly is likely to happen? Will I be in pain?”)

During a home visit three weeks before this woman passed away, Dr. Meier asked her what was on her mind. “She said, ‘I am really upset this doctor has not called me or come to see me.’ It was taking up most of her emotional energy.”

With the patient’s permission, Dr. Meier called the physician, whose response was, “There’s nothing I can do for her.” Dr. Meier had to explain: “She loves you. She wants to thank you.” That got through: the oncologist made a visit, and the patient died a few days later.

Mrs. Rieger has stayed in touch with Dr. Geynisman during the year since her husband’s death; she doesn’t blame the physician in any way. “He was our guiding light and he never disappointed us,” she told me. “Dan made the whole year so bearable, because I knew there was someone there for us.” The doctor, she noted, never let more than 10 minutes lapse before answering an email.

“He was the one person who knew our cancer journey better than anyone else,” Mrs. Rieger said. “He became so important to us. He touched our souls.”

Currently, Dr. Geynisman is an assistant professor of medical oncology at Fox Chase Cancer Center in Philadelphia. “I’m committed to being there through the end with all my patients, though I still haven’t figured out the best way to do that,” he said.

To his patients, he puts it something like this: “I’m still your physician and no matter what happens, I’m still here for you.”