If you had a serious illness, how much would you want to know about it?

Dr. Rachel A. Freedman, an oncologist who specializes in breast cancer at the Dana Farber Cancer Institute in Boston, said she noticed a few years ago that many patients who were referred to her had little understanding of their disease or its treatment.

There was hardly any published information on what patients knew about their own cancers, so Dr. Freedman and some colleagues decided to conduct a study. They asked 500 women four questions: Did they know the stage of their tumor, the grade (an indicator of how aggressive a cancer is), and whether it was fed by estrogen or a growth factor called HER-2?

“Nobody’s ever looked at this before, and it’s a simple set of questions,” she said.

The researchers compared the women’s answers with their medical records. The results, published in January in the journal Cancer, showed that a little more than half of the women knew their cancer’s stage and its estrogen and HER-2 status. Only 20 percent knew the grade. Blacks and Hispanics tended to know less than whites.

The study did not determine why the patients knew so little. “It’s hard to know if doctors aren’t discussing it, or if patients aren’t hearing it,” Dr. Freedman said.

Having the information can matter, because many breast cancers are curable if women stick with their treatment, she said. If patients do not know how important treatment is, they may be more likely to quit, particularly if side effects are harsh.

But there is a world of difference between hearing about treatments that can save your life and hearing that they have failed. When cancer is advanced and people fear that death is looming, they are more likely to prefer being spared the details, Dr. Freedman said.

Still, she added, even among the sickest, “I think most patients do want to know.”

Recognizing that aggressive therapy no longer holds promise allows some patients to switch to treatments aimed at keeping them comfortable.

But people who have been dealt a bad hand have different ways of playing it.

Stuart Scott, the ESPN anchor who died of cancer in January, said a year ago that he did not know his prognosis.

“I never ask what stage I’m in,” he said in an interview with The New York Times. “I haven’t wanted to know. It won’t change anything to me. All I know is that it would cause more worry and a higher degree of freakout. Stage 1, 2 or 8, it doesn’t matter. I’m trying to fight it the best I can.”

Medical schools have tried harder to train doctors to deliver bad news without crushing the patient. But a recent study suggests that even the kindest manner may not soften the blow as much as expected.

At the University of Texas MD Anderson Cancer Center in Houston, researchers showed 100 patients with advanced cancer videos of two doctors speaking separately to a sad-looking woman with late-stage cancer who asked if there was some new chemotherapy that would help her.

The doctors and patient were actors, and the videos were crafted to insure that the doctors’ tone, facial expressions, manner and body language were warm and identical. The only difference was the doctors’ message — one was more optimistic than the other.

In one video, the doctor told the patient that no more chemo was possible “right now,” but that if she started feeling a little better, “we can find something for you.”

In the other video, the doctor said no more chemo was possible, and “there is no serious chance of curing your cancer.”

The patients were asked to rate how compassionate and trustworthy the doctors were. The one who offered the more optimistic message scored higher. The findings were published in February in JAMA Oncology.

“What we wanted to test here was, would just the message itself cause you to see me as more or less compassionate?” said Dr. Eduardo Bruera, the senior author of the study and chairman of palliative care and rehabilitation medicine at MD Anderson. “We had a feeling that the ‘shooting the messenger’ idea was present.”

He said medical students are taught that if they are empathetic and use the right body language, patients will see them as compassionate.

“We thought the appropriate methodology might protect us like a shield,” Dr. Bruera said. “Unfortunately, the message itself has some effect.”

It’s not surprising that people don’t like bad news, though the reaction does not mean that patients don’t want the truth. Eighty percent do want to know, he said.

Does it matter if this discussion puts some distance between doctor and patient? Dr. Bruera said he suspected that doctors felt the chill and were distressed about having to provide bad news, and that this might be contributing to high rates of burnout in his specialty.

More studies are being planned, he said, in hopes of finding ways to tell the truth that will be less painful to both doctors and patients.

A version of this article appears in print on March 17, 2015, on page D4 of the New York edition with the headline: What Patients Prefer to Know.

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