C11.1 ICD-10-CM Code: Malignant neoplasm of posterior wall of nasopharynx
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
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 guidanceMalignant 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 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.
CMS-HCC V28
MappedHCC 21
RAF 0.545
CMS-HCC V24
MappedHCC 11
RAF 0.306
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 11
RAF 0.0
RXHCC
00
RAF 0
Code Trumping
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Code Book Path
Inclusion Terms
Official- Malignant neoplasm of adenoid
- Malignant neoplasm of pharyngeal tonsil
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for C11.1 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for C11.1 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for C11.1 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for C11.1 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
OfficialICD-10-CM does not list Code Also instructions for C11.1 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is C11.1 an HCC code?
Yes. C11.1 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for C11.1
For C11.1to 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 C11.1 during that encounter, not just copy-forwarded from a problem list.
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 Breast, Prostate, Colorectal and Other Cancers and Tumors (HCC 21) with a community, non-dual, aged base RAF weight of 0.545. Under the older CMS-HCC V24 model, C11.1 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.306. 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.
Verify the specific anatomical location is documented as posterior wall to distinguish from other nasopharyngeal sites. Because C11.1 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 C11.1 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