What is ICD-10 code C11.9?

C11.9 is the ICD-10-CM diagnosis code for Malignant neoplasm of nasopharynx, unspecified. Cancer of the nasopharynx when the specific location within this area is not documented or specified. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C11.9 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C11.9 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C11.9 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C11.9 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for C11.9?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C11.9, V28 maps to Lymphoma and Other Cancers at RAF 0.671 while V24 mapped to Colorectal, Bladder, and Other Cancers at RAF 0.307. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C11.9?

Use this code only when the exact site (posterior, lateral, or anterior wall) cannot be determined from documentation Query the provider if possible to obtain more specific anatomical location for accurate coding Because C11.9 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM C11.9: Malignant neoplasm

ICD-10-CM Code View

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Code lookupC11.9Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C11.9

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

Malignant neoplasm of nasopharynx, unspecified

Cancer of the nasopharynx when the specific location within this area is not documented or specified.

Buddy Insight

Malignant neoplasm of nasopharynx, unspecified, is used when the specific nasopharyngeal wall cannot be determined.

CMS-HCC V28

Mapped

HCC 21

Lymphoma and Other Cancers

RAF 0.671

CMS-HCC V24

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.307

ACA/HHS

Mapped

HCC 11

HHS-HCC 11

Varies by metal level

ESRD/PACE

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.059

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

C11Malignant neoplasm of nasopharynx

C11.9Malignant neoplasm of nasopharynx, unspecified

Inclusion Terms

Official

Malignant neoplasm of nasopharyngeal wall NOS

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C11.9 in this effective period.

Related Child Codes

Official

C11.0Malignant neoplasm of superior wall of nasopharynx

C11.1Malignant neoplasm of posterior wall of nasopharynx

C11.2Malignant neoplasm of lateral wall of nasopharynx

C11.3Malignant neoplasm of anterior wall of nasopharynx

C11.8Malignant neoplasm of overlapping sites of nasopharynx

Includes

Official

ICD-10-CM does not list Includes notes for C11.9 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C11.9 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C11.9 in this effective period.

Use Additional

Official

code to identify:
exposure to environmental tobacco smoke (Z77.22)
exposure to tobacco smoke in the perinatal period (P96.81)
history of tobacco dependence (Z87.891)
occupational exposure to environmental tobacco smoke (Z57.31)

Code Also

Official

ICD-10-CM does not list Code Also instructions for C11.9 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirmation of nasopharyngeal malignancy

Documentation of imaging review for wall-specific information

EBV status

Provider query documentation for specific anatomical detail

MEAT Support

HCC Buddy guidance

Pathology confirmation of nasopharyngeal malignancy

Documentation of imaging review for wall-specific information

EBV status

Provider query documentation for specific anatomical detail

Audit Caution

HCC Buddy guidance

Using this code without checking MRI or endoscopy reports that typically specify the involved wall

Not querying the radiation oncologist or ENT specialist who will have specific site information

Confusing nasopharynx (upper throat behind nose) with oropharynx (middle throat behind mouth) or hypopharynx (lower throat)

Accepting a general diagnosis of 'nasopharyngeal cancer' without pursuing wall-specific documentation

Common Mistakes

HCC Buddy guidance

C11.1 — Posterior wall; the most common nasopharyngeal cancer site — check imaging

C11.2 — Lateral wall; second most common site — check for Eustachian tube involvement

C14.0 — Pharynx, unspecified; even less specific — at least C11.9 identifies the nasopharynx

C11.8 — Overlapping sites; use when multiple walls are involved but identifiable

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 C11.9 an HCC code?

Yes. C11.9 (Malignant neoplasm of nasopharynx, unspecified) maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24), with a community non-dual aged RAF of 0.671. It is billable for payment year 2026.

Coder answer: C11.9 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: C11.9
Description: Malignant neoplasm of nasopharynx, unspecified
HCC (V28): HCC 21 — Lymphoma and Other Cancers
RAF: 0.671
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers

0.671

V24HCC 11, Colorectal, Bladder, and Other Cancers

0.307

ESRDHCC 11, Colorectal, Bladder, and Other Cancers

0.059

Each model's RAF is its CMS base weight for that model's standard population, so 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 segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work C11.9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C11.9

For C11.9 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

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

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C11.9 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C11.9 is the ICD-10-CM diagnosis code for malignant neoplasm of nasopharynx, unspecified. Cancer of the nasopharynx when the specific location within this area is not documented or specified. C11.9 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, C11.9 maps to Lymphoma and Other Cancers (HCC 21) with a community, non-dual, aged base RAF weight of 0.671. Under the older CMS-HCC V24 model, C11.9 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.307. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Use this code only when the exact site (posterior, lateral, or anterior wall) cannot be determined from documentation. Because C11.9 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for C11.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use this code only when the exact site (posterior, lateral, or anterior wall) cannot be determined from documentation
•Query the provider if possible to obtain more specific anatomical location for accurate coding

Clinical Significance

Malignant neoplasm of nasopharynx, unspecified, is used when the specific nasopharyngeal wall cannot be determined. Given that modern MRI staging and endoscopy can typically identify the involved wall(s), this code should prompt review of imaging reports before assignment.

Documentation Requirements

✓Pathology confirmation of nasopharyngeal malignancy
✓Documentation of imaging review for wall-specific information
✓EBV status
✓Provider query documentation for specific anatomical detail
✓Complete staging and treatment information

Commonly Confused Codes

•C11.1: Posterior wall; the most common nasopharyngeal cancer site: check imaging
•C11.2: Lateral wall; second most common site: check for Eustachian tube involvement
•C14.0: Pharynx, unspecified; even less specific: at least C11.9 identifies the nasopharynx
•C11.8: Overlapping sites; use when multiple walls are involved but identifiable