Enhertu (fam-trastuzumab deruxtecan-nxki) — HCPCS J9358

Dosing matrix by indication FDA label verified May 2026

Enhertu has two distinct dose levels depending on tumor type. Confirm dose before mixing.

Infusion timing — cycle 1 vs cycles 2+

• Cycle 1: infuse over 90 minutes. Bill 96413 + 96415 × 1.
• Cycles 2+ if cycle 1 tolerated: infuse over 30 minutes. Bill 96413 only.
• Slow or stop infusion for any infusion-related reaction; resume per institutional protocol.

Worked unit-math example — 70 kg HER2+ breast (5.4 mg/kg q3w)

Worked example — 80 kg HER2+ gastric (6.4 mg/kg q3w)

HER2 biomarker tiers — HER2+, HER2-low, HER2-ultralow CAP/ASCO + FDA verified May 2026

Enhertu's label expansion has redefined how oncology bills HER2. Three different cutpoints unlock three different patient populations.

NDC reference FDA NDC Directory verified May 2026

Administration codes CPT verified May 2026

Enhertu is billed as chemotherapy administration despite being an ADC.

Modifiers CMS verified May 2026

JW — required on virtually every Enhertu claim

Because Enhertu is dosed by weight and ships only as a 100 mg single-dose vial, partial-vial waste is the rule. Bill the discarded portion on a separate J9358 claim line with the JW modifier. Example: a 70 kg patient at 5.4 mg/kg needs 378 mg → 4 vials drawn (400 mg) → 22 mg waste. Two lines: 378 units with JZ + 22 units with JW.

JZ — on the administered-units line

Effective July 1, 2023, CMS requires either JZ (no waste) or JW (waste) on every single-dose container claim. For Enhertu, the administered-units line carries JZ; the waste line carries JW. One of JZ or JW must be on every J9358 claim.

Modifier 25 — same-day E/M

Use modifier 25 on the E/M code when a significant, separately identifiable evaluation and management service is performed on the same day as the infusion (e.g., ILD assessment visit). Routine pre-infusion clinical assessment is bundled.

340B modifiers (JG, TB)

For 340B-acquired Enhertu, follow your MAC's current 340B modifier policy. Daiichi Sankyo's billing guide does not provide 340B-specific instructions.

ICD-10-CM by indication FY2026 verified May 2026

Six approved indication groups. Use the most specific code supported by encounter documentation. Tumor-agnostic indication uses the site-specific C-code plus HER2 IHC 3+ documentation.

Site of care & place of service Verified May 2026

UnitedHealthcare, Aetna, and most major BCBS plans run aggressive site-of-care UM for high-cost oncology biologics. Enhertu falls squarely in scope. After the first few cycles (and once ILD risk is being actively monitored), commercial plans steer Enhertu out of HOPD into office or AIC settings.

Claim form field mapping Daiichi Sankyo / AstraZeneca AccessSupport 2026

From the Enhertu HCP coding & coverage materials and AstraZeneca AccessSupport billing guide.

Payer policy snapshot Reviewed May 2026

All major payers require HER2 documentation matched to the requested indication's HER2 tier. Get the path report in hand before submitting PA.

HER2 biomarker test billing (separate from drug claim)

Step therapy

Generally required for HER2+ breast (must demonstrate progression on a prior HER2-directed therapy, typically T-DM1 or trastuzumab + pertuzumab) and for HER2+ gastric (prior trastuzumab-based regimen). HER2-low and HER2-ultralow require prior chemotherapy in the metastatic setting. Tumor-agnostic indication requires documentation of prior systemic therapy and no satisfactory alternative. Verify per payer.

Medicare reimbursement CMS Q2 2026 (live)

Quarterly ASP from CMS Part B Drug Pricing File. Refreshes automatically each quarter.

Coverage

No NCD specific to fam-trastuzumab deruxtecan-nxki. Coverage falls under MAC LCDs for biologics + the generic drug-coverage framework. All MACs cover J9358 for FDA-approved on-label indications with appropriate ICD-10 and HER2 biomarker documentation.

Code history

• J9358 — permanent code, "Inj fam-trastu deru-nxki 1mg" (initial FDA approval was December 2019; pre-permanent-code period used unclassified J3490 / J9999)
• Indication expansions occur 1-2 times per year; most recent additions: HER2-ultralow breast (2025), tumor-agnostic accelerated (2024)

Patient assistance — AstraZeneca AccessSupport / Daiichi Sankyo PAN Verified May 2026

• AstraZeneca AccessSupport (Enhertu hub): 1-833-340-2462 / azaccesssupport.com — benefits investigation, prior authorization assistance, appeal support
• Daiichi Sankyo Patient Access Network: co-development partner program, additional reimbursement support
• Enhertu Co-Pay Savings Program: commercial copay support up to $25,000/year for eligible commercially-insured patients (excludes Medicare, Medicaid, federal program patients)
• Patient Assistance Program (PAP): free product for uninsured / underinsured patients meeting income requirements
• Foundations: for Medicare patients, refer to PAN Foundation, HealthWell, CancerCare — verify open breast/gastric/lung oncology funds quarterly
• Web: azaccesssupport.com / enhertu.com

ILD monitoring & documentation FDA boxed warning — verified May 2026

Required documentation for payer audits

• Baseline imaging (chest CT) prior to cycle 1 with documented absence of pre-existing ILD/pneumonitis
• Pulmonary symptom screen at every cycle (cough, dyspnea, fever, hypoxia)
• Imaging on suspicion of any new pulmonary symptoms — HRCT preferred
• ILD work-up for any imaging finding: pulmonology consult, infectious work-up to exclude pneumonia, consideration of bronchoscopy
• Hold/discontinue documentation matched to grade (Grade 1 hold; Grade 2+ permanent discontinuation)

Steroid management for confirmed ILD

• Per FDA label: prompt initiation of corticosteroids (typically prednisone 0.5-1 mg/kg/day or equivalent for Grade 1; 1-2 mg/kg/day for Grade 2+)
• Slow taper over weeks once symptoms resolve
• Document steroid course for chart and any future PA submissions for alternative therapy

Common denials & how to fix them

Frequently asked questions

What is the HCPCS code for Enhertu?

Enhertu (fam-trastuzumab deruxtecan-nxki) is billed under HCPCS J9358 — "Inj fam-trastu deru-nxki 1mg." Each milligram equals one billable unit. Dosing is weight-based: 5.4 mg/kg q3w for HER2+ breast, HER2-low breast, HER2-ultralow breast, HER2-mutant NSCLC, and HER2+ tumor-agnostic; 6.4 mg/kg q3w for HER2+ gastric/GE junction. The drug ships as a 100 mg single-dose lyophilized vial.

How many units do I bill for an Enhertu dose?

Enhertu dosing is weight-based, so units = patient mg actually administered. Examples: 70 kg patient × 5.4 mg/kg = 378 mg dose = 378 units. 70 kg × 6.4 mg/kg = 448 mg dose = 448 units. The drug comes in 100 mg single-dose vials, so partial-vial waste is virtually always present — bill the administered dose in mg as units (JZ line) plus any wasted mg as a separate claim line with JW modifier.

What administration CPT do I use for Enhertu?

CPT 96413 (chemo IV, first hour) plus 96415 (each additional hour) for cycle 1 only (90-minute infusion). Cycles 2+ use only 96413 (30-minute infusion if cycle 1 was tolerated). Enhertu is a complex monoclonal antibody-drug conjugate billed under chemo admin codes per CPT/AMA classification. Do NOT bill 96365 (therapeutic IV).

Do I bill JZ or JW for Enhertu?

Almost every Enhertu claim needs both: JZ on the administered-units line and JW on the waste-units line. Because dosing is weight-based and the only available vial is 100 mg, partial-vial waste is the rule, not the exception. Example: 70 kg patient at 5.4 mg/kg needs 378 mg → 4 vials drawn (400 mg) → 22 mg waste. Bill 378 units with JZ + 22 units with JW.

What is the Medicare reimbursement for J9358?

For Q2 2026, the Medicare Part B payment limit for J9358 is $31.262 per mg (ASP + 6%). For a 70 kg patient at 5.4 mg/kg (378 mg administered + 22 mg waste = 400 mg billed), reimbursement is approximately $12,504.80 per cycle. Annualized at q3w (~17 cycles/year): approximately $212,582. After ~2% sequestration: roughly $208,300/year actual paid.

What HER2 biomarker tests are required for Enhertu?

All Enhertu indications require a documented HER2 result, but the threshold differs: HER2+ (IHC 3+ or 2+/ISH+) for HER2+ breast, gastric/GEJ, NSCLC, and tumor-agnostic indications. HER2-low (IHC 1+ or 2+/ISH-) for HER2-low metastatic breast. HER2-ultralow (IHC 0 with membrane staining) for HER2-ultralow metastatic breast. HER2-mutant NSCLC additionally requires NGS showing an activating HER2 mutation (typically exon 20 insertion). Schedule HER2 IHC/ISH/NGS BEFORE submitting Enhertu PA.

What is the boxed warning on Enhertu?

Enhertu carries TWO boxed warnings. (1) Interstitial lung disease (ILD)/pneumonitis — severe, sometimes fatal cases reported in approximately 12% of patients. Monitor cough, dyspnea, fever, hypoxia. Hold for any suspected ILD. Permanently discontinue for Grade 2+ ILD/pneumonitis. (2) Embryo-fetal toxicity — verify pregnancy status and counsel on contraception. Document baseline imaging and ongoing pulmonary monitoring for payer audits.

Does Enhertu have a tumor-agnostic indication?

Yes — Enhertu carries an accelerated FDA approval for HER2-positive (IHC 3+) unresectable or metastatic solid tumors that have progressed on prior systemic therapy and have no satisfactory alternative treatment options. The tumor-agnostic indication may require NCCN-alignment documentation in the prior authorization, plus HER2 IHC 3+ result and a documented prior line of therapy. Use the site-specific C-code plus HER2 documentation.

Source documents

1. AstraZeneca AccessSupport — Enhertu Coding & Billing HCP page
   Document footer: AZ AccessSupport 2026
2. DailyMed — ENHERTU (fam-trastuzumab deruxtecan-nxki) Prescribing Information
   FDA-approved label, most recent revision (BLA 761139, label updated frequently with new indications)
3. FDA Drugs@FDA — Enhertu BLA 761139 supplements & approvals
   Includes HER2-low (2022), HER2+ NSCLC (2022), tumor-agnostic accelerated (2024), HER2-ultralow (2025)
4. CMS — Medicare Part B Drug ASP Pricing File
   Q2 2026 quarterly file, effective April 1 – June 30, 2026
5. SEER CanMED — HCPCS J9358 reference
6. UnitedHealthcare — Oncology Medication Clinical Coverage Policy
7. Aetna CPB — HER2-targeted therapies (covers fam-trastuzumab deruxtecan-nxki)
8. NCCN Guidelines — Breast, Gastric, NSCLC (HER2 sections)
   For tumor-agnostic indication PA, NCCN compendium reference is often required
9. AstraZeneca AccessSupport patient hub (1-833-340-2462)
10. FDA National Drug Code Directory

About this page

We maintain this page as a living reference. Medicare ASP pricing is bound to our underlying CareCost data layer and refreshes automatically when CMS publishes new quarterly files. Coding and policy content is reviewed at least quarterly and updated whenever a source document changes. Enhertu's label is one of the most rapidly expanding in oncology — expect indication additions 1-2× per year.

Found an error? Email hello@carecostestimate.com.

Refresh cadence

Reviewer

Change log

• May 2, 2026 — Initial publication. ASP data: Q2 2026. Manufacturer source: AstraZeneca AccessSupport 2026 / Daiichi Sankyo. FDA label: most recent revision. Six approved indications including HER2-ultralow breast (2025) and HER2+ tumor-agnostic accelerated (2024). Two boxed warnings (ILD/pneumonitis ~12%; embryo-fetal toxicity).

Methodology

Every claim on this page is sourced inline. Pricing reflects the current CMS Part B Drug ASP Pricing File. Payer policies are read directly from each payer's published medical/pharmacy policy documents. Indication list and HER2 tier definitions are verified against the current FDA label revision. We do not paraphrase from billing-software vendor blogs.