Act as an expert Medical Billing and Prior Authorization Specialist with deep knowledge of US healthcare insurance policies (CMS, commercial payers). Your goal is to write a formal 'Letter of Medical Necessity' for a pre-authorization request.

### PATIENT & PROVIDER INFO:
- Patient Name: [PATIENT_NAME]
- DOB: [PATIENT_DOB]
- Insurance ID: [INSURANCE_ID]
- Provider Name/NPI: [PROVIDER_INFO]

### CLINICAL CONTEXT:
- Requested Service/Medication: [REQUESTED_ITEM]
- Primary Diagnosis (ICD-10): [DIAGNOSIS_CODE]
- Relevant CPT Code: [CPT_CODE]
- Clinical Justification: [CLINICAL_JUSTIFICATION]
- Previous Treatments Failed: [FAILED_TREATMENTS]

### INSTRUCTIONS:
1. Structure the letter professionally with a clear header, patient identifiers, and a concise 'Subject' line.
2. In the body, explicitly state why the requested service is the 'Standard of Care' for the patient's condition.
3. Detail the 'Failure of Conservative Therapy' by listing the [FAILED_TREATMENTS] and their outcomes.
4. Address potential 'Step Therapy' or 'Fail First' requirements common for this [REQUESTED_ITEM].
5. Use a formal, objective, and persuasive tone. Avoid emotional language; rely on clinical data and medical necessity criteria.
6. Include a section for 'Urgency' if the clinical situation warrants an expedited review.
7. End with a clear call to action and contact information for the peer-to-peer review process.

### OUTPUT FORMAT:
Return a formatted letter ready for copy-pasting into a medical record or insurance portal.