After breast-conserving surgery (lumpectomy), the standard adjuvant local therapy is?

• A. Postoperative external beam radiation therapy to the breast
• B. Observation without therapy
• C. Chemotherapy only
• D. Hormonal therapy

Answer: (B)

Breast-conserving surgery removes the tumor but leaves microscopic disease in the remaining breast tissue, so delivering local control with radiation is essential. Postoperative external beam radiation therapy to the breast is the standard adjuvant local treatment after lumpectomy. It targets the whole breast (with a possible boost to the tumor bed) to sterilize residual cancer cells and markedly reduce the risk of local recurrence, which improves long-term outcomes. Systemic therapies like chemotherapy or hormonal therapy address micrometastatic disease and distant recurrence, not the local breast tissue, and observation would leave residual disease untreated.