My friend’s mother got terrifying news after she had a mammogram. She had Stage 0 breast cancer.  Cancer: That dreadful word.  Of course she had to have surgery to get it out of her breast followed by hormonal therapy. Or did she? Though it is impossible to say whether the treatment was necessary in this case, one thing is growing increasingly clear to many researchers: The word “cancer” is out of date, and all too often it can be unnecessarily frightening.  The word “cancer” is used, these experts say, for far too many conditions that are very different in their prognoses — from “Stage 0 breast cancer,” which may be harmless if left alone, to glioblastomas, brain tumors with a dismal prognosis no matter what treatment is tried.

Now, some medical experts have recommended getting rid of the word “cancer” altogether for certain conditions that may or may not be potentially fatal. The idea of cancer as a progressive disease that will kill if the cells are not destroyed dates back to the 19th century, said Dr. Otis Brawley, chief scientific and medical officer at the American Cancer Society. A German pathologist, Rudolph Virchow, examined tissue taken at autopsy from people who had died of their cancers, looking at the cells under a light microscope and drawing pictures of what he saw.

Virchow was a spectacular artist, and he ended up being the first to describe a variety of cancers — leukemia, breast cancer, colon cancer, lung cancer.  Of course, his patients were dead.  So when he noted that “aberrant-looking” cells will kill, it made sense. The deranged cells were cancers, and cancers were fatal.

Now, Dr. Brawley said, the situation is very different. Instead of taking tissue from someone who died, a doctor takes tissue from a living patient, threading a thin needle into a woman’s breast or a man’s prostate, for example. Then a pathologist looks for abnormal cells.  Yet “how it looks under a microscope, Dr. Brawley said, does not always predict.” That is especially true for things like Stage 0 breast cancer or similar conditions in other areas of the body — conditions detected by screening and not by symptoms or by feel. Researchers have come to appreciate this conundrum.  “The definition of cancer has changed,” said Dr. Robert Aronowitz, a professor of history and sociology of medicine at the University of Pennsylvania. Many medical investigators now speak in terms of the probability that a tumor is deadly. And they talk of a newly recognized risk of cancer screening — over diagnosis.

Screenings can find what are actually harmless, abnormal-looking clusters of cells. But since it is not known for sure whether they will develop into fatal cancers, doctors tend to treat them with the same methods that they use to treat clearly invasive cancers. Screening is finding “cancers” that did not need to be found. So maybe “cancer” is not always the right word for them.

That happened recently with Stage 0 breast cancer, also known as ductal carcinoma in situ, or D.C.I.S.  It is a small accumulation of abnormal-looking cells inside the milk ducts of the breast. There’s no lump, nothing to be felt. In fact, Stage 0 was almost never detected before the advent of mammography screening. Now, with widespread screening, this particular diagnosis accounts for about 20 percent of all breast cancers. That is, if it actually is cancer. After all, it is confined to a milk duct, has not spread into the rest of the breast, and may never spread if left alone — it might even go away. It could also break free and enter the breast tissue. But for now, it is hard to know in many cases whether it makes any difference to treat D.C.I.S. right away or to wait to see if it spreads, and treating it then.

Two years ago, an expert panel at the National Institutes of Health said the condition should be renamed. Get rid of the loaded word “carcinoma,” the panel said. A carcinoma is invasive; D.C.I.S. has not invaded the breast. If those cells do invade, they are no longer D.C.I.S.  Then they are cancer.  So call the condition something else, perhaps “high-grade dysplasia.”

The word “cancer” is so powerful it overwhelms any conversation about what Stage 0 breast cancer actually is, said Cynthia Pearson, executive director of the National Women’s Health Network. When women contact her group to ask about cancer treatments, “sometimes we’re well into the conversation with them before it comes out that they don’t actually have an invasive cancer.”

The same situation arises with prostate cancer screening. The pathologist Donald Gleason, who invented Gleason scoring for prostate tumors, wanted to rename a very common tumor — the so-called Gleason 3 + 3 — “adenosis” instead of cancer, Dr. Brawley said. His idea was that by calling a 3 + 3 “cancer,” men and their doctors would feel they had to get rid of it right away. Despite Dr. Gleason’s wishes, 3 + 3 cells are still called cancer. And despite the panel’s advice about D.C.I.S., that name has not changed either.

Cervical cancer specialists had better luck. In 1988, they changed the name of a “sort of” Stage 0 of the cervix. It had been called cervical carcinoma in situ. They renamed it cervical intraepithelial neoplasia, Grades 1 to 3, taking away the cancer connotation. But Dr. Brawley, for one, has not given up on educating doctors and patients about the general inadequacy of the word “cancer.” As he put it, “The movement is not quite dead.”

Let us hope for its quick demise.