**Core Concept:** Sentinel Node Biopsy (SNB) is a minimally invasive surgical technique used in breast cancer staging to identify the first lymph node(s) draining the tumor. It is done to determine if cancer has spread to the lymph nodes. The procedure involves injecting a radioactive tracer and/or a blue dye near the tumor, which allows the surgeon to identify the sentinel node(s) during surgery.

**Why the Correct Answer is Right:** During a SNB procedure, a nerve responsible for sensation in the breast is also damaged. In this case, the correct answer is C: **Axillary Nerve**.

The axillary nerve is a branch of the C5-C7 spinal nerves that supplies motor and sensory innervation to the skin, subcutaneous tissue, and muscles of the upper limb. In the axilla, the axillary nerve branches into anterior (anterior cutaneous branch) and posterior (posterior cutaneous branch) divisions. The anterior division supplies sensation to the skin of the upper limb, including the breast. Thus, damage to the axillary nerve during SNB can result in sensory deficits in the area served by this nerve, including the breast.

**Why Each Wrong Option is Incorrect:**

A. The radial nerve (C5-C7) is not involved in sensation for the breast, making it an incorrect answer.

B. The brachial plexus (C5-C8) is responsible for sensory innervation of the upper limb but not specific to the breast, making it an incorrect answer.

D. The internal mammary nerve (C5-C8) is not involved in sensation for the breast, making it an incorrect answer.

**Clinical Pearl:** It is essential for surgeons performing SNB to be aware of the axillary nerve's location to minimize potential complications, such as sensory deficits in the breast. Early recognition and management of these complications can improve patient outcomes and satisfaction post-surgery.