Which prior medical history is considered a high-risk criterion for breast cancer?

• A. Dense breast tissue
• B. Atypical ductal hyperplasia
• C. Prior chest radiation therapy
• D. 5-year Gail model risk ≥1.7%

Answer: (C)

Prior chest radiation therapy is a well-established high-risk factor for breast cancer. When radiation is given to the chest, especially at a young age, it increases the lifetime risk of developing breast cancer manyfold because ionizing radiation can induce malignant changes in breast tissue over time. This risk is strong enough that screening guidelines recommend intensified surveillance, typically starting MRI screening years earlier (often 8–10 years after radiation or by age 25, whichever comes later) in addition to mammography, and continuing throughout life.

Dense breast tissue, while it can modestly raise relative risk, is considered more a risk modifier than a standalone high-risk history for initiating enhanced screening. Atypical ductal hyperplasia is indeed associated with higher cancer risk, but it is a histologic finding rather than a historical exposure; it guides risk assessment but isn’t the classic prior medical history used to label someone as high risk in screening guidelines. The 5-year Gail model risk ≥1.7% reflects calculated risk, not a specific past medical history.