**Core Concept**
The **TNM staging system** is used to classify the extent of spread of cancer, with T describing the size of the primary tumor, N describing the presence and extent of lymph node involvement, and M describing the presence of metastasis. In breast cancer, the size of the tumor and the involvement of axillary lymph nodes are crucial for staging.

**Why the Correct Answer is Right**
A 6 cm breast cancer with fixed ipsilateral axillary lymph nodes would be classified as **T3** due to the size of the tumor and **N2** due to the fixed axillary lymph nodes, indicating a more advanced stage of cancer. This combination corresponds to a specific stage in the TNM staging system.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not accurately reflect the size of the tumor or the extent of lymph node involvement.
**Option B:** Incorrect as it underestimates the extent of disease given the tumor size and lymph node fixation.
**Option D:** Incorrect because it does not correctly represent the combination of tumor size and lymph node status for this scenario.

**Clinical Pearl / High-Yield Fact**
In breast cancer staging, the presence of fixed axillary lymph nodes indicates a more advanced disease and affects treatment planning and prognosis. Remembering the TNM staging criteria is crucial for determining the appropriate stage and guiding management decisions.

**Correct Answer: C. T3 N2**