2026 ICD-10-CM Diagnosis Code C11.1Malignant neoplasm of posterior wall of nasopharynx

ICD-10-CM Codes›C00–D49›C00-C14›C11

ICD-10-CM C11.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

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 146 through 148. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Head and neck cancers - nasopharyngeal.

Code Identity

ICD-10-CM Code
C11.1
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neoplasm of posterior wall of nasopharynx
Short Description
Malignant neoplasm of posterior wall of nasopharynx
Same as the full description in the CMS dataset.
Parent Code
C11
Malignant neoplasm of nasopharynx

Code Classification

ChapterC00–D49Neoplasms
SectionC00-C14Malignant neoplasms of lip, oral cavity and pharynx
CategoryC11Malignant neoplasm of nasopharynx
This CodeC11.1Malignant neoplasm of posterior wall of nasopharynx

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

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO005
Head and neck cancers - nasopharyngeal
Default principal diagnosis: inpatient Yes · outpatient Yes

Table of NeoplasmsClinical

Anatomical sites in the Table of Neoplasms that reference this code family.

SiteMalig.
Primary		Malig.
Secondary		Ca
in situ		BenignUncertainUnspec.
adenoid (pharynx) (tissue)C11.1C79.89D00.08D10.6D37.05D49.0
nasopharynx, nasopharyngeal › wall › posteriorC11.1C79.89D00.08D10.6D37.05D49.0
pharynx, pharyngeal › bursaC11.1C79.89D00.08D10.6D37.05D49.0
pharynx, pharyngeal › tonsilC11.1C79.89D00.08D10.6D37.05D49.0
tonsil › pharyngealC11.1C79.89D00.08D10.6D37.05D49.0

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.

ICD-9-CM
147.1 Mal neo post nasopharynx
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C11.1Overview

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 146, 147, 148, with relative weights from 0.7971 to 2.1174 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.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.