**Core Concept**
Routine screening mammography is a widely accepted practice for early detection of breast cancer in asymptomatic women. The optimal age for initiating this screening has been a topic of debate among healthcare professionals. The decision is based on the balance between the benefits of early detection and the risks associated with radiation exposure, false positives, and unnecessary biopsies.

**Why the Correct Answer is Right**
The American Cancer Society recommends routine screening mammography starting at age 45 to 54 years, with the option to begin at age 40 years for women who are at higher risk. The American College of Radiology also supports the initiation of screening mammography at age 40 years. This decision is based on evidence suggesting that the benefits of early detection, such as reduced mortality rates, outweigh the risks for women in this age group. The **mammography screening guidelines** are tailored to the individual's risk factors, including family history, genetic predisposition, and personal history of breast cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** Screening mammography at age 20 years is not recommended due to the low incidence of breast cancer in this age group and the potential for false positives and unnecessary biopsies.
**Option B:** Starting screening mammography at age 30 years may delay the detection of breast cancer, potentially reducing the effectiveness of treatment and increasing mortality rates.
**Option D:** Recommending routine screening mammography at age 50 years may be too late for some women, as breast cancer can be more aggressive and harder to treat in older age groups.

**Clinical Pearl / High-Yield Fact**
Women with a family history of breast cancer, particularly those with a first-degree relative diagnosed before age 50 years, should consider starting screening mammography at age 40 years or 10 years before the age of diagnosis of the affected relative, whichever comes first.

**✓ Correct Answer: C. 40 years**