**Core Concept**
Cetuximab is a monoclonal antibody that acts as an epidermal growth factor receptor (EGFR) antagonist. This means it blocks the binding of epidermal growth factor (EGF) to EGFR, thereby inhibiting cell proliferation and angiogenesis in various cancers.

**Why the Correct Answer is Right**
Cetuximab is used in the treatment of certain types of cancer, particularly those with overexpression of EGFR. It works by competitively binding to the extracellular domain of EGFR, preventing the ligand (EGF) from binding and activating the receptor. This leads to decreased cell proliferation, increased apoptosis, and reduced angiogenesis. Cetuximab has been shown to be effective in the treatment of colorectal cancer, head and neck cancer, and skin cancer (squamous cell carcinoma).

**Why Each Wrong Option is Incorrect**
**Option A:** Cetuximab is not typically used for the treatment of breast cancer, as it has not been shown to be effective in this population.
**Option B:** While cetuximab is an EGFR antagonist, it is not primarily used for the treatment of non-small cell lung cancer (NSCLC), which is more commonly treated with EGFR tyrosine kinase inhibitors (TKIs).
**Option C:** Cetuximab is not typically used for the treatment of ovarian cancer, as it has not been shown to be effective in this population.

**Clinical Pearl / High-Yield Fact**
Cetuximab is a type of monoclonal antibody that targets the extracellular domain of EGFR, making it a useful treatment option for cancers with EGFR overexpression.

**Correct Answer: D. Squamous cell carcinoma of the skin**