By Counterforce Health Team in Enhertu (fam-trastuzumab deruxtecan-nxki) —

Coding That Helps Get Enhertu (fam-trastuzumab deruxtecan-nxki) Approved with Humana in California: ICD-10, J-Code, and NDC Guide

Quick Answer: Coding for Enhertu (fam-trastuzumab deruxtecan-nxki) Approval

Getting Enhertu covered by Humana in California requires precise coding: ICD-10 Z17.31 (HER2-positive status) paired with your cancer diagnosis (C50.-, C16.-, C34.-), J-code J9358 (1 mg units), and NDC 65597-0406-01. Submit prior authorization through Humana's Availity portal with HER2 pathology reports, treatment history, and medical necessity documentation. If denied, file internal appeal within 65 days, then escalate to California's Independent Medical Review (IMR) through DMHC for binding external review.

First step today: Verify your Humana formulary tier and gather HER2 test results before your oncologist submits the PA request.

Table of Contents

Coding Basics: Medical vs. Pharmacy Benefit

Enhertu (fam-trastuzumab deruxtecan-nxki) is an IV infusion therapy that typically falls under medical benefit rather than pharmacy benefit for Humana Medicare Advantage plans. This means:

  • Billing path: Provider-administered (buy-and-bill) through medical claims
  • Prior authorization: Required through Humana's medical PA process, not pharmacy
  • Coverage tier: Specialty Tier 4 with network restrictions (often Accredo for oncology)
Note: Some Humana plans may route specialty infusions through pharmacy benefit. Verify your specific plan's coverage determination via member services.

The coding pathway determines approval speed. Medical benefit claims require:

  • Proper diagnosis sequencing (primary cancer first, then HER2 status)
  • Accurate J-code and unit calculations
  • Supporting documentation for medical necessity

ICD-10 Mapping for HER2-Positive Cancers

Primary Diagnosis Codes

Code first the underlying malignancy, then add HER2 status:

Cancer Type Primary ICD-10 Common Specifics
Breast Cancer C50.- C50.911 (right), C50.912 (left), C50.919 (unspecified)
Gastric/GEJ C16.- C16.0 (cardia), C16.2 (body), C16.9 (unspecified)
NSCLC C34.- C34.10 (upper lobe), C34.30 (lower lobe), C34.90 (unspecified)

HER2 Status Documentation

Required secondary code: Z17.31 - Human epidermal growth factor receptor 2 positive status (effective October 1, 2024)

Enhanced options for detailed receptor status:

  • Z17.410: Hormone receptor positive + HER2 positive (breast cancer)
  • Z17.420: Hormone receptor negative + HER2 positive (breast cancer)

Documentation Requirements

Your pathology report must include specific language supporting Z17.31:

  • "HER2 3+ by IHC" or "HER2 amplified by FISH/ISH"
  • "HER2-positive" or "HER2 overexpression"
  • For NSCLC: "HER2 mutation" (not just overexpression)
Tip: If pathology shows "HER2 2+ pending FISH," wait for final results before coding Z17.31. Equivocal results may not support coverage.

Product Coding: J-Code, NDC, and Units

HCPCS J-Code: J9358

J9358 - Injection, fam-trastuzumab deruxtecan-nxki, 1 mg (permanent since July 1, 2020)

Unit calculation examples:

  • 70 kg patient × 5.4 mg/kg = 378 mg = 378 units
  • 80 kg patient × 6.4 mg/kg = 512 mg = 512 units

NDC Number: 65597-0406-01

Product details:

  • 100 mg lyophilized powder, single-dose vial
  • Bill with 11-digit NDC: 65597-0406-01
  • Units designation: "UN1" (unit of 1)

Dosing by Indication

Indication Dose Max Units/Cycle Frequency
Breast Cancer 5.4 mg/kg ~600 units Every 21 days
Gastric/GEJ 6.4 mg/kg ~700 units Every 21 days
NSCLC 5.4 mg/kg ~600 units Every 21 days
Important: Bill actual mg administered, not vial contents. Waste units are typically not separately billable.

Clean Request Anatomy

Sample Prior Authorization Request

Patient: 65-year-old female, metastatic HER2+ breast cancer
Plan: Humana Medicare Advantage California

Primary Diagnosis: C50.911 (Malignant neoplasm of right breast)
Secondary: Z17.31 (HER2-positive status)
Procedure: J9358 × 378 units (5.4 mg/kg × 70 kg)
NDC: 65597-0406-01
Frequency: Every 21 days × 6 cycles initially

Required Documentation Checklist

✅ HER2 Testing: IHC 3+ or FISH/ISH amplification report
✅ Prior Therapies: Trastuzumab + pertuzumab progression notes
✅ Staging: Metastatic disease confirmation (imaging)
✅ Performance Status: ECOG 0-2 documentation
✅ Cardiac Function: LVEF ≥50% if prior anthracyclines
✅ ILD Screening: Baseline chest CT ruling out interstitial lung disease

Frequent Coding Pitfalls

Unit Conversion Errors

❌ Wrong: Billing by vial (100 units) instead of actual dose
✅ Correct: Calculate patient-specific mg dose, then convert to units

❌ Wrong: Using legacy J9999 code
✅ Correct: Use permanent J9358 (effective since 2020)

Missing Documentation

❌ Wrong: "HER2 positive" without test method
✅ Correct: "HER2 3+ by IHC" or "HER2 amplified, ratio 2.5 by FISH"

❌ Wrong: Generic "failed prior therapy"
✅ Correct: "Progressive disease on trastuzumab + pertuzumab after 4 cycles, documented by CT scan [date]"

Diagnosis Sequencing

❌ Wrong: Z17.31 listed first
✅ Correct: Primary cancer (C50.911) first, then Z17.31

Humana Verification Steps

Check Formulary Status

  1. Log into Humana provider portal or call provider services
  2. Verify: Enhertu formulary tier (typically Tier 4 Specialty)
  3. Confirm: Network specialty pharmacy requirements (often Accredo)
  4. Review: Current prior authorization list for oncology drugs

Prior Authorization Submission

Preferred method: Availity provider portal (95% decisions within 1 business day targeted for 2026)

Alternative methods:

  • CoverMyMeds for pharmacy PA
  • Fax: Provider-specific number (verify current)
  • Phone: For urgent cases requiring expedited review

Timeline Expectations

  • Standard PA: ~7 days
  • Expedited: 72 hours for urgent cases
  • New enrollees: No PA required for first 90 days if continuing pre-enrollment treatment

Pre-Submission Audit Checklist

Coding Review

  • Primary cancer diagnosis coded to highest specificity
  • Z17.31 included as secondary diagnosis
  • J9358 units match calculated patient dose
  • NDC 65597-0406-01 included with UN1 designation

Documentation Completeness

  • HER2 pathology report with specific test results
  • Prior therapy history with dates and outcomes
  • Current staging and performance status
  • Baseline cardiac and pulmonary function
  • Medical necessity letter addressing Humana criteria

Submission Details

  • Correct provider NPI and facility information
  • Patient insurance ID and group number verified
  • Requested cycle count and frequency specified
  • Site of care appropriate for infusion therapy

Appeals Process in California

If your Enhertu request is denied, California offers robust appeal rights through both Humana's internal process and state-level external review.

Internal Appeal with Humana

Timeline: File within 65 days of denial notice
Process: Submit through Humana provider portal or mail
Decision time: 30-60 days standard, 72 hours expedited

Required documents:

  • Original denial letter
  • Updated medical necessity letter
  • Additional clinical evidence (new imaging, lab results)
  • Peer-reviewed literature supporting off-label use (if applicable)

California Independent Medical Review (IMR)

After Humana upholds the denial, California residents can request binding external review through the Department of Managed Health Care (DMHC).

Success rate: 55-73% approval for specialty cancer drug appeals
Timeline: 45 days standard, 72 hours expedited for life-threatening cases
Cost: Free to patients

How to file:

  1. Submit online: healthhelp.ca.gov
  2. Call DMHC Help Center: 1-888-466-2219 (24/7)
  3. Include all records: Denial letters, medical records, supporting literature
From our advocates: "We've seen strong IMR success rates when appeals include recent progression imaging, detailed prior therapy timelines, and citations from NCCN guidelines or FDA labeling. The key is showing medical necessity under the plan's own criteria, not just clinical benefit."

When to Escalate Further

For Medicare Advantage plans, you may also have federal appeal rights:

  • Medicare appeals: Contact Livanta at 1-877-588-1123
  • State insurance complaint: File with DMHC if plan violates timelines

FAQ

Q: How long does Humana prior authorization take for Enhertu in California?
A: Standard PA decisions average 7 days. Humana targets 95% of electronic submissions (via Availity) within 1 business day by 2026. Expedited reviews for urgent cancer cases are decided within 72 hours.

Q: What if Enhertu is non-formulary on my Humana plan?
A: You can request a formulary exception through the PA process. Include documentation that formulary alternatives have failed or are contraindicated. California's step therapy override laws support exceptions when alternatives aren't appropriate.

Q: Can I request an expedited appeal if my cancer is progressing?
A: Yes. Both Humana and California IMR offer expedited reviews for life-threatening conditions. Include oncologist documentation of disease progression and urgency of treatment initiation.

Q: Does the new Z17.31 code affect existing approvals?
A: Existing approvals should continue, but new requests after October 1, 2024, should use Z17.31 for HER2-positive status. This provides more specific coding that may actually strengthen PA requests.

Q: What if I'm switching from another HER2-targeted therapy?
A: Document the reason for switch (progression, intolerance, contraindication) with specific dates and clinical evidence. Humana's new enrollee protection covers continuing therapies for 90 days while PA is processed.

Q: How do I verify my oncology provider is in Humana's network?
A: Use Humana's online provider directory or call member services. For specialty infusions like Enhertu, also verify the infusion center is contracted for outpatient chemotherapy administration.

Counterforce Health helps patients and clinicians navigate complex prior authorization requirements for specialty medications like Enhertu. Our platform analyzes denial letters and payer policies to create targeted, evidence-backed appeals that address specific coverage criteria. By combining clinical documentation with payer-specific workflows, we help turn insurance denials into approvals while reducing administrative burden on healthcare providers.

Sources & Further Reading

Disclaimer: This information is for educational purposes only and does not constitute medical or legal advice. Coverage policies and coding requirements may change. Always verify current requirements with Humana and consult healthcare professionals for treatment decisions. For personalized assistance with prior authorizations and appeals, consider working with Counterforce Health or other qualified patient advocacy services.

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