The Register Citizen (Torrington, CT)
Yale study: Small cancers less dangerous because they’re small
NEW HAVEN » The use of mammography to find small breast cancer tumors may be overrated, because most of those cancers will grow so slowly that early detection does not increase survival rates, according to a Yale Cancer Center study.
More aggressive cancers, usually characterized by a larger-sized tumor, often will not be detected by a mammogram before they are large enough to be physically felt, according to Dr. Donald R. Lannin, professor of surgery at the Yale School of Medicine and lead author of the paper, which was published Wednesday in the New England Journal of Medicine.
“For over 100 years, we’ve known that small [breast] cancers have a better prognosis than large breast cancers, and we always thought that it was because they were being detected earlier,” Lannin said.
As it turns out, he said, “That’s somewhat of an illusion. It’s not really so important. … The reason that small cancers have such a good prognosis is because they were good all along and they won’t get big.” He called these tumors “indolent, slow-growing cancers … They would never grow to cause a problem.”
Early detection of them is actually a case of overdiagnosis, write Lannin and Dr. Shiyi Wang in the journal. Wang is assistant professor of epidemiology at the Yale School of Public Health.
A factor in the increase in over-diagnosing slowgrowing cancers are that “radiologists now are so good that they are finding tiny, little cancers in a big breast,” Lannin said.
“So many women are scared unduly because they end up with a tiny little indolent cancer that would take 20 years to grow large enough for the patient to feel it in the breast. … The most indolent, slow-growing ones are so slow-growing that most of them will never get big enough to be palpable,” Lannin said.
That time period between detection by mammography and being able to feel a lump is called its lead time. Lannin said doctors once believed that the lead time for all cancers was about the same, about three or four years. But Lannin and Wang’s study showed that “actually there’s tremendous variability in the growth rate of cancers,” Lannin said, with the growth rate of small tumors at 15 to 20 years, and the rate for large tumors at less than two years.
For large tumors, that means that, most often, by the time they are detected in a mammogram they would have been felt by physical examination. “That’s what people hadn’t really realized,” Lannin said.
Rather than size, the important factor is the biology of the tumor. “There’s good breast cancers and bad breast cancers and the good breast cancers grow very, very slowly and the bad breast cancers grow very quickly,” Lannin said.
In their study, Lannin and Wang looked at cancers diagnosed between 2001 and 2013 and divided them into three groups based on grade, their estrogen-receptor status and their progesterone-receptor status, taken from the national database of the National Cancer Institute’s Surveillance, Epidemiology and End Results Program. There are four grades of cancer, each of which “correlates with how fast the cancer grows,” according to Lannin.
“There were 12 combinations of these variables, each with a distinct prognosis,” according to their paper, with four combinations in each group. Lannin called those groups “the favorable, the intermediate and the unfavorable.”
The smaller tumors tended to fall into the favorable group, while large tumors tend to be the most unfavorable.
“In a group of patients, we can say pretty accurately which ones are overdiagnosed,” Lannin said. “If they are very favorable, we don’t need to treat them so aggressively with chemotherapy and radiation.” A lumpectomy will be all that is needed, he said.
“One caveat I should say is, in an individual patient we can never say 100 percent that a cancer is overdiagnosed. It depends on the biology,” as well as factors such as whether the cancer involves the lymph nodes.
Because small tumors grow so slowly, “early detection is not as important as we used to think and the biology is the most important thing that indicates the prognosis. There’s a huge variability in the biology, that some cancers are very favorable and grow very slowly and other cancers are very aggressive and grow very quickly, so the degree of variability is much greater than we used to think,” Lannin said. “It’s really this great variability that causes the misdiagnosis.”
Lannin said he is not advising women to shun mammograms, although annual procedures are not as highly recommended as they once were. The American Cancer Society recommends a mammogram every year for women between 45 and 54 years old, and every two years after that, given an average family history and good health.
Lannin said, however, that his research helps explain why mammograms only reduce the death rate from cancer by 19 percent “and not by 75 percent or 80 percent, like you might think it would.”
Also, because aggressive cancers can be physically felt by the time a mammogram would see them, “it might be worth stopping mammograms by age 70 or 75,” Lannin said. “Many of the cancers you’d find at that age are the favorable ones that are over-diagnosed.”