Overdiagnosis in breast screening: the honest debate

Overdiagnosis happens when screening finds a real breast cancer, confirmed under the microscope, that would never have caused symptoms or harm during a woman's lifetime. This can happen because some cancers, particularly some cases of ductal carcinoma in situ and some slow-growing invasive cancers, grow so slowly or remain so stable that the woman would have lived out her life without ever knowing about them, or would have died of something else first. Overdiagnosis is different from a false positive. In a false positive, there is no cancer. In overdiagnosis, there is a genuine cancer, but finding and treating it does not help the woman, and she may experience surgery, radiation or hormone treatment, with their side effects, anxiety and cost, without benefit. The difficulty is that doctors cannot currently tell, for an individual woman, which screen-detected cancers are overdiagnosed and which would have become dangerous. So nearly all are treated. Estimates of how common overdiagnosis is vary widely between studies, because it cannot be measured directly and different methods give different answers. The debate is not about whether screening has value. Mammography screening has been shown to reduce breast cancer deaths in women of screening age. The debate is about how to balance that benefit against overdiagnosis and false alarms, and how to give women honest information to make informed choices.

Overdiagnosis finds real but harmless cancers

These would never have caused problems if left undiscovered.

It cannot be identified in one person

Doctors cannot yet say which cancers are overdiagnosed, so most are treated.

Screening still saves lives

The debate is about the balance of benefits and harms, not about abandoning screening.

This is one of the more uncomfortable topics in cancer screening, and honesty matters.

Estimates vary widely

Different studies use different methods, so figures for how common overdiagnosis is range from small to substantial.

No test yet separates harmless from harmful

Research into markers and genomic tests continues, but none can reliably pick out overdiagnosed cancers today.

The Indian picture may differ

In India, many cancers are still found late, so the balance of benefits and harms may not match countries with long-running programmes.

What this page cannot tell you

It cannot tell you whether a cancer found in you is overdiagnosed. Your specialist can explain the features of your own diagnosis.

Researchers are working on ways to keep the benefits of screening while reducing its harms.

Risk-based screening

Studies are testing whether screening intervals tailored to each woman's risk can improve the balance.

Active monitoring trials

Trials in several countries are comparing careful monitoring with surgery for selected low-risk DCIS.

Better biological tests

Research into genomic profiles aims to identify which cancers are likely to stay harmless.