This article appears in Paint it Pink 2017.

Highly trained radiologists can detect small cancers so early through mammography that there now may be an overdiagnosis of small tumors, which can lead to unnecessary treatment, according to a Yale Cancer Center study.

“Radiologists are so skilled at finding tiny little tumors. It’s the price we pay. They’re finding a lot of small cancers that will never become large and life-threatening,” said Dr. Donald Lannin, professor of surgery at Yale School of Medicine and lead author on the paper.

Many small cancers have an excellent prognosis because they are inherently slow-growing and treatable, such as with a lumpectomy, Lannin said. Early detection doesn’t necessarily increase survival rates because these cancers will not grow large enough to become significant within a patient’s lifetime, he said.

In contrast, large tumors that cause most breast cancer deaths often grow so quickly that they become dangerous before they can be detected by screening mammography.

Diagnosis not a death sentence

Before mammography it was thought that all cancers were life-threatening, and if cancer was detected earlier — when it was smaller — it would lead to higher survival rates, Lannin said.

Yet today mammograms only decrease breast cancer mortality rates by 19 percent, Lannin said.

“We would expect it to be higher, maybe 50 or 75 percent. We hoped for three decades to cut the risk by more,” he said.

As the science of mammography has accelerated diagnosis, radiologists are detecting “three times the amount of small cancers,” many of which are not life-threatening, Lannin said.

Previously, the medical community knew that there were differences in tumor growth rates but thought that the differences were small. What’s new from the Yale study is, researchers found that a large percentage of cancers grow quickly and another large percentage of cancers grow slowly, Lannin said.

“There’s a lot of bad breast cancers and also a lot of good breast cancers,” Lannin said. The diverse character of breast cancer explains both how mammography leads to overdiagnosis and also why it is not more effective.

What you should know

“Women shouldn’t have an over-optimistic expectation that a mammogram will keep you from dying from breast cancer,” Lannin said. Often, aggressive cancers can be physically felt before a mammogram can detect them, Lannin said.

He does not suggest women skip mammograms. Instead, they should “have some perspective” when faced with a diagnosis of a small breast cancer tumor, “which probably has a pretty good prognosis,” Lannin said.

The American Cancer Society suggests women 45 to 54 schedule a mammogram every year and after age 55 every two years, depending on health and family history.

Beyond that, treatment depends on the age of the patient and the biology of the cancer, Lannin said.

For a woman in her 50s diagnosed with a small slow-growing tumor, the cancer probably would have been diagnosed in her 70s without mammography, Lannin said. But a woman in her 70s diagnosed with a small slow-growing tumor may die of something else before the cancer grows large enough to be detected or be life-threatening, Lannin said.

The biology of the breast cancer also determines its treatment, Lannin said. Treatment depends on factors such as grade (how fast it grows), hormone receptors (how favorable the status of the estrogen and progesterone receptors are) and molecular testing. Those things determine how aggressively the cancer should be treated, Lannin said.