Breast Cancer Screening May Not Be as Harmful as Thought

Topic: Health

Researchers from Denmark and London studied breast cancer screening trials to understand how often cancers are detected that would never have caused harm. They found that previous estimates of overdiagnosis may have been too high, suggesting that only a small percentage of cancers detected through screening are not life-threatening.

Breast cancer screening can sometimes identify cancers that would never have caused symptoms or threatened a woman's health during her lifetime. This is known as overdiagnosis.

For decades, researchers have debated how often overdiagnosis actually occurs. Estimates from randomized trials have differed sharply, with some studies suggesting that 30-50% of breast cancers detected through screening could fall into this category. These figures have influenced international discussions about the benefits and possible harms of population-based breast cancer screening.

A team of researchers led by Sisse Helle Njor, a professor at University of Southern Denmark and Lillebælt Hospital, wanted to get a clearer picture of the extent of overdiagnosis in breast cancer screening. They combined and reanalyzed results from all randomized trials of mammography screening and compared them with data from Denmark.

Denmark was a useful reference because organized breast cancer screening began in some regions 17 years earlier than in others. This allowed researchers to track how breast cancer diagnoses changed immediately after screening was introduced and how those patterns evolved over longer periods.

The researchers found that the additional breast cancer cases detected in randomized trials closely resembled patterns seen in Denmark, where overdiagnosis associated with screening is estimated to be below 5%. They also discovered that previous high estimates of overdiagnosis may have been based on evidence before trial data had fully matured.

Why It Matters

This study has implications for breast cancer screening policies and guidelines. If only a small percentage of cancers detected through screening are not life-threatening, it could mean that more women can benefit from early detection without unnecessary harm.

Key Facts

• Researchers studied breast cancer screening trials to understand how often cancers are detected that would never have caused harm.
• Previous estimates of overdiagnosis ranged from 30-50%, but this study suggests the actual number may be much lower, below 5%.
• The study used data from Denmark, where organized breast cancer screening began in some regions 17 years earlier than in others.
• The researchers found that the additional breast cancer cases detected in randomized trials closely resembled patterns seen in Denmark.
• This study has implications for breast cancer screening policies and guidelines.

Key Terms

Overdiagnosis

When a screening test detects a cancer that would never have caused symptoms or threatened health during lifetime.

Implications

This study has implications for breast cancer screening policies and guidelines. If only a small percentage of cancers detected through screening are not life-threatening, it could mean that more women can benefit from early detection without unnecessary harm.