Identification of the Fraction of Indolent Tumors and Associated Overdiagnosis in Breast Cancer Screening Trials

Finding and treating very slow-growing cancers through aggressive screening doesn’t help people live longer overall — it just finds cancers that wouldn’t have hurt them anyway.

Some cancers found during routine screening might never hurt you — they grow so slowly that you’d die of something else before they ever became a problem.

When scientists try to figure out how fast breast cancer grows and how many tumors are slow-moving, their calculations get less accurate if the numbers they use for slow-growing tumors or fast-growing tumors are too low or too high.

If doctors don't keep an eye on breast cancer patients long enough after their last screening, they can't tell how fast the cancer is likely to grow — it's like trying to guess how long a candle will burn by only watching it for a few seconds.

If doctors keep checking on women longer after their last breast cancer screening, they can better tell which tumors would never cause harm and which ones are likely to grow quickly—especially when cancers tend to develop slowly.

When doctors stop screening for breast cancer, they can't tell exactly how many of the tumors found would never have caused harm, even with fancy math, because the data they have just isn't detailed enough to give clear answers.