Which of the following is an indication for radiation therapy after a modified radical mastectomy?

• A. Negative surgical margins
• B. Positive surgical margins
• C. Small tumor size
• D. Less than 4 positive axillary lymph nodes

Answer: (B)

Radiation therapy after a modified radical mastectomy is indicated in cases with positive surgical margins. Positive surgical margins indicate that cancer cells are present at the edge of the removed tissue, suggesting that the tumor may not have been completely excised. This increases the risk of local recurrence, making additional treatment necessary to reduce that risk. Radiation therapy helps to target any remaining cancer cells in the breast or in the chest wall area, improving the patient's overall prognosis and reducing the likelihood of cancer returning.

The other factors mentioned, such as negative surgical margins, small tumor size, and having fewer than four positive axillary lymph nodes, do not typically indicate the need for adjuvant radiation therapy in the same way. Negative surgical margins suggest that the tumor has been adequately removed, while a small tumor size or a limited number of positive lymph nodes may not present the same level of concern for local recurrence, thus often leading to different treatment strategies that may not include radiation therapy.