**Core Concept**
The American Cancer Society recommends various cancer screening tests for different age groups to detect and prevent cancer. The guidelines consider factors such as the risk of cancer, the sensitivity and specificity of the screening test, and the potential harms associated with testing.

**Why the Correct Answer is Right**
For a 25-year-old woman, the American Cancer Society recommends regular cervical cancer screening with a Pap test (or high-risk human papillomavirus (HPV) testing) starting at age 21, regardless of the age of initiation of sexual activity. Screening for breast cancer with mammography is not recommended for women under 40 years of age due to the low incidence of breast cancer in this age group and the potential harms associated with radiation exposure.

**Why Each Wrong Option is Incorrect**
**Option A:** Mammography is not recommended for women under 40 years of age due to the low incidence of breast cancer in this age group and the potential harms associated with radiation exposure.
**Option B:** Colon cancer screening with colonoscopy is recommended starting at age 50 years, so it is not recommended for a 25-year-old woman.
**Option C:** Lung cancer screening with low-dose computed tomography (LDCT) is recommended for current or former smokers aged 55 to 74 years with a 30-pack-year smoking history, so it is not recommended for a 25-year-old woman who quit smoking 7 years ago.

**Clinical Pearl / High-Yield Fact**
For women aged 21 to 29 years, cervical cancer screening should be performed every 3 years with a Pap test (or high-risk HPV testing), and women aged 30 to 65 years can choose between a Pap test and an HPV test every 5 years.

**Correct Answer:** C. Cervical cancer screening with a Pap test (or high-risk human papillomavirus (HPV) testing) starting at age 21.