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C11.1 ICD-10-CM Code: Malignant neoplasm of posterior wall of nasopharynx

C11.1 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools

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Code lookupC11.1

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lip, oral cavity and pharynx (C00-C14)

C11.1

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Malignant neoplasm of posterior wall of nasopharynx

Cancer that starts in the back wall of the nasopharynx, which is the upper part of the throat behind the nose.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of the posterior wall of the nasopharynx is the most common site for nasopharyngeal carcinoma, a cancer with unique epidemiology concentrated in Southern China, Southeast Asia, and North Africa.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 21

Coefficient HCC 21: 0.671 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 011

Code-level coefficient reference

ESRD/PACE

HCC 11

Code-level coefficient reference

RXHCC

N/A

—

Not mapped

Code Book Path

Official
C11Malignant neoplasm of nasopharynxC11.1Malignant neoplasm of posterior wall of nasopharynx

Inclusion Terms

Official
  • Malignant neoplasm of adenoid
  • Malignant neoplasm of pharyngeal tonsil

Excludes 2

Official

No Excludes 2 notes are included in this display for C11.1. Check the code and parent instructions in the Code Book.

Related Codes

Official
C11.0Malignant neoplasm of superior wall of nasopharynxC11.2Malignant neoplasm of lateral wall of nasopharynxC11.3Malignant neoplasm of anterior wall of nasopharynxC11.8Malignant neoplasm of overlapping sites of nasopharynxC11.9Malignant neoplasm of nasopharynx, unspecified

Includes

Official

No Includes notes are included in this display for C11.1. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for C11.1. Check the code and parent instructions in the Code Book.

Code First

Official

No Code First sequencing instructions are included in this display for C11.1. Check the code and parent instructions in the Code Book.

Use Additional

Official
  • code to identify:Inherited from C11
  • exposure to environmental tobacco smoke (Z77.22)Inherited from C11
  • exposure to tobacco smoke in the perinatal period (P96.81)Inherited from C11
  • history of tobacco dependence (Z87.891)Inherited from C11
  • occupational exposure to environmental tobacco smoke (Z57.31)Inherited from C11
  • tobacco dependence (F17.-)Inherited from C11
  • tobacco use (Z72.0)Inherited from C11

Code Also

Official

No Code Also instructions are included in this display for C11.1. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Pathology-confirmed malignancy with WHO classification (Type I, II, or III)
EBV status including plasma EBV DNA levels
Documentation specifying posterior wall of nasopharynx
MRI of nasopharynx and skull base for staging

MEAT Support

HCC Buddy guidance
Pathology-confirmed malignancy with WHO classification (Type I, II, or III)
EBV status including plasma EBV DNA levels
Documentation specifying posterior wall of nasopharynx
MRI of nasopharynx and skull base for staging

Audit Caution

HCC Buddy guidance
Confusing posterior wall of nasopharynx (C11.1) with posterior wall of oropharynx (C10.3) — different anatomical levels of the throat
Not documenting WHO histological classification which is unique to nasopharyngeal carcinoma
Using unspecified nasopharynx code when the posterior wall is clearly documented on MRI or endoscopy
Missing EBV testing which is essential for nasopharyngeal carcinoma diagnosis and surveillance

Common Mistakes

HCC Buddy guidance
C11.0 — Superior wall of nasopharynx; the posterior wall is the back surface, distinct from the roof
C11.2 — Lateral wall of nasopharynx; the posterior wall is midline, the lateral walls are on the sides
C10.3 — Posterior wall of oropharynx; ensure the tumor is in the nasopharynx (behind nose) not oropharynx (behind mouth)
C11.9 — Nasopharynx, unspecified; avoid when posterior wall is documented

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C11.1 an HCC code?

Yes. C11.1 (Malignant neoplasm of posterior wall of nasopharynx) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C11.1 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C11.1
Description
Malignant neoplasm of posterior wall of nasopharynx
HCC (V28)
HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient
0.671
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers
0.671
ESRDHCC 11, Colorectal/Bladder/and Other Cancers
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C11.1 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C11.1

For C11.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

  • MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
  • EEvaluate: test results, medication response, or physical findings reviewed by the provider
  • AAssess: explicit mention in the assessment or plan with acknowledgment of status
  • TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Coder workflow notes

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What This Code Means

C11.1 is the ICD-10-CM diagnosis code for malignant neoplasm of posterior wall of nasopharynx. Cancer that starts in the back wall of the nasopharynx, which is the upper part of the throat behind the nose. C11.1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lip, oral cavity and pharynx (c00-c14).

Under the CMS-HCC V28 risk adjustment model, C11.1 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. No V24 mapping is shown for C11.1; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Verify the specific anatomical location is documented as posterior wall to distinguish from other nasopharyngeal sites. For C11.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for C11.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Verify the specific anatomical location is documented as posterior wall to distinguish from other nasopharyngeal sites
  • •This location is common in patients with history of Epstein-Barr virus infection or tobacco/alcohol use

Clinical Significance

Malignant neoplasm of the posterior wall of the nasopharynx is the most common site for nasopharyngeal carcinoma, a cancer with unique epidemiology concentrated in Southern China, Southeast Asia, and North Africa. EBV is a key etiologic factor, and plasma EBV DNA is used for monitoring treatment response and detecting recurrence.

Documentation Requirements

  • ✓Pathology-confirmed malignancy with WHO classification (Type I, II, or III)
  • ✓EBV status including plasma EBV DNA levels
  • ✓Documentation specifying posterior wall of nasopharynx
  • ✓MRI of nasopharynx and skull base for staging
  • ✓Assessment of cranial nerve involvement (particularly CN V and VI)

Commonly Confused Codes

  • •C11.0: Superior wall of nasopharynx; the posterior wall is the back surface, distinct from the roof
  • •C11.2: Lateral wall of nasopharynx; the posterior wall is midline, the lateral walls are on the sides
  • •C10.3: Posterior wall of oropharynx; ensure the tumor is in the nasopharynx (behind nose) not oropharynx (behind mouth)
  • •C11.9: Nasopharynx, unspecified; avoid when posterior wall is documented

Child Codes

C11.0Malignant neoplasm of superior wall of nasopharynx
HCC 21
C11.1Malignant neoplasm of posterior wall of nasopharynx
HCC 21
C11.2Malignant neoplasm of lateral wall of nasopharynx
HCC 21
C11.3Malignant neoplasm of anterior wall of nasopharynx
HCC 21
C11.8Malignant neoplasm of overlapping sites of nasopharynx
HCC 21
C11.9Malignant neoplasm of nasopharynx, unspecified
HCC 21

Code Hierarchy

└C11Malignant neoplasm of nasopharynx└C11.1Malignant neoplasm of posterior wall of nasopharynx
└C11.1Malignant neoplasm of posterior wall of nasopharynx

Also searched as

  • C11 1
  • C111

For C11.1, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

C11.1 maps to CMS-HCC V28 category 21, Lymphoma and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C11.1. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

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Open C11.1 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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