2026 ICD-10-CM Diagnosis Code C11.1Malignant neoplasm of posterior wall of nasopharynx
ICD-10-CM Codes›C00–D49›C00-C14›C11
- Billable — Valid for Submission
- Risk Adjusts — HCC 21
- Chronic Condition
C11.1 is a billable ICD-10-CM diagnosis code for malignant neoplasm of posterior wall of nasopharynx. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 11 through 13, 146 through 148. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Head and neck cancers - nasopharyngeal.
For Medicare Advantage risk adjustment, C11.1 maps to CMS-HCC Category 21 (Lymphoma and Other Cancers) under the V28 model, adding a risk factor of about 0.671 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C11.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Adenoid squamous cell carcinoma of nasopharynx
- Malignant neoplasm of adenoid
- Malignant neoplasm of posterior wall of nasopharynx
- Neoplasm of adenoid
- Primary malignant neoplasm of adenoid
- Primary malignant neoplasm of posterior wall of nasopharynx
- Primary malignant neoplasm of Waldeyer's ring
- Primary squamous cell carcinoma of pharyngeal tonsil
- Primary squamous cell carcinoma of posterior wall of nasopharynx
- Primary squamous cell carcinoma of Waldeyer ring
- Primary undifferentiated carcinoma of nasopharynx
- Primary undifferentiated carcinoma of posterior wall of nasopharynx
- Squamous cell carcinoma of posterior wall of nasopharynx
- Undifferentiated carcinoma of nasopharynx
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Malignant neoplasm of adenoid
- Malignant neoplasm of pharyngeal tonsil
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Table of NeoplasmsClinical
Anatomical sites in the Table of Neoplasms that reference this code family.
| Site | Malig. Primary | Malig. Secondary | Ca in situ | Benign | Uncertain | Unspec. |
|---|---|---|---|---|---|---|
| adenoid (pharynx) (tissue) | C11.1 | C79.89 | D00.08 | D10.6 | D37.05 | D49.0 |
| nasopharynx, nasopharyngeal › wall › posterior | C11.1 | C79.89 | D00.08 | D10.6 | D37.05 | D49.0 |
| pharynx, pharyngeal › bursa | C11.1 | C79.89 | D00.08 | D10.6 | D37.05 | D49.0 |
| pharynx, pharyngeal › tonsil | C11.1 | C79.89 | D00.08 | D10.6 | D37.05 | D49.0 |
| tonsil › pharyngeal | C11.1 | C79.89 | D00.08 | D10.6 | D37.05 | D49.0 |
Patient EducationClinical
Throat Cancer
Throat cancer is a type of head and neck cancer. Throat cancer has different names, depending on which part of the throat is affected. The different parts of your throat are called the oropharynx, the hypopharynx, the nasopharynx, and the larynx, or voice box.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert C11.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C11.1Overview
What is the ICD-10 code for malignant neoplasm of posterior wall of nasopharynx?
The ICD-10-CM code for malignant neoplasm of posterior wall of nasopharynx is C11.1 (sometimes written as C111). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is C11.1 (Malignant neoplasm of nasopharynx) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report malignant neoplasm of posterior wall of nasopharynx on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does C11.1 group to?
When malignant neoplasm of posterior wall of nasopharynx is the principal diagnosis on an inpatient stay, it groups to MS-DRG 11, 12, 13, 146, 147, 148, with relative weights from 0.7971 to 5.4541 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of C11.1?
Under the General Equivalence Mappings, malignant neoplasm of posterior wall of nasopharynx converts to ICD-9-CM 147.1 (mal neo post nasopharynx). The mapping is a direct match.
What HCC is C11.1?
C11.1 (malignant neoplasm of posterior wall of nasopharynx) maps to CMS-HCC Category 21 (Lymphoma and Other Cancers), commonly written as HCC 21, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 11 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does C11.1 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C11.1 adds a risk adjustment factor of about 0.671 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.493 to 0.739 depending on the payment segment). A more severe related category (HCC 17, HCC 18, HCC 19, and HCC 20) supersedes it when both are reported. See the full factor table on the HCC 21 category page.
