Overdetection of Breast Cancer

Area of Science:

• Oncology
• Preventive Medicine
• Biostatistics

Background:

• Overdetection, or overdiagnosis, involves identifying cancers that would never have become clinically apparent or caused death.
• The primary harm stems from unnecessary overdiagnosis and subsequent overtreatment.
• Screening programs can lead to detecting indolent or slow-growing cancers.

Purpose of the Study:

• To review the phenomenon of cancer overdetection.
• To discuss methods for estimating overdetection and reasons for variability.
• To analyze overdetection using Canadian data and microsimulation modeling.

Main Methods:

• Review of the phenomenon of cancer overdetection.
• Discussion of estimation methods and sources of variability.
• Microsimulation modeling to illustrate cancer detection timelines.

Main Results:

• Overdetection is a real phenomenon but likely occurs at a lower rate than previously estimated.
• The significance of overdetection is greater in older women due to competing mortality risks.
• In situ breast cancer presents a particular challenge for overdetection and overtreatment.

Conclusions:

• While overdetection exists, its prevalence may be lower than often cited.
• Age and competing causes of death significantly influence the impact of overdetection.
• Strategies to mitigate overtreatment, especially for in situ breast cancer, are needed.