American Board of Internal Medicine (ABIM) Certification Practice Exam

Recommending radiation after mastectomy is often influenced by the status of tumor margins. When there are positive tumor margins, it indicates that cancerous cells may still be present at the edges of the surgically removed tissue. This raises the concern for local recurrence of the disease, making additional treatment necessary to reduce this risk. Radiation therapy aims to target and eliminate any remaining cancer cells in the chest wall or nearby lymph nodes, significantly lowering the chance of cancer returning.

In the context of other answers, tumors measuring less than 2 cm typically might not necessitate radiation therapy if there are no other adverse characteristics, such as high-grade features or positive margins. The presence of benign breast tissue does not directly influence the need for radiation therapy after mastectomy. Lastly, the absence of axillary involvement (meaning that cancer has not spread to the lymph nodes in the underarm area) may also suggest a lower risk of recurrence, further arguing against the routine need for radiation in such cases. Thus, the presence of positive tumor margins is the critical factor that prompts the recommendation for radiation post-mastectomy.