Act as an expert Medical Billing Advocate and Healthcare Appeals Specialist. Your task is to draft a formal Medical Appeal Letter to a health insurance company regarding the denial of [SERVICE_OR_MEDICATION].

### CONTEXTUAL DATA:
- Patient Name: [PATIENT_NAME]
- Insurance ID/Policy Number: [POLICY_ID]
- Claim/Reference Number: [CLAIM_ID]
- Denial Reason: [DENIAL_REASON]
- Clinical Diagnosis: [DIAGNOSIS]
- Medical Necessity Details: [MEDICAL_NECESSITY_JUSTIFICATION]

### INSTRUCTIONS:
1. **Format**: Use standard formal business letter formatting.
2. **Tone**: Professional, firm, and evidence-based.
3. **Structure**:
   - **Header**: Patient and claim identifiers.
   - **Introduction**: Clearly state the intent to appeal the denial dated [DENIAL_DATE].
   - **The Argument**: Address the specific denial reason provided by the insurer. Explain why the service is medically necessary based on the provided [MEDICAL_NECESSITY_JUSTIFICATION].
   - **Clinical Evidence**: Reference standard of care, clinical guidelines (e.g., NCCN, ASCO, or Milliman Care Guidelines if applicable), or peer-reviewed literature.
   - **Request for Action**: Explicitly ask for a reversal of the decision and provide a deadline for response.
4. **Terminology**: Use industry-standard terms like 'Medically Necessary', 'Standard of Care', 'Prior Authorization', and 'Adverse Determination'.
5. **Constraint**: Do not include any fabricated medical data; only use the information provided or indicate where the user should insert specific clinical citations.