2026 ICD-10-CM Diagnosis Code C09.0Malignant neoplasm of tonsillar fossa

ICD-10-CM Codes›C00–D49›C00-C14›C09

ICD-10-CM C09.0
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C09.0 is a billable ICD-10-CM diagnosis code for malignant neoplasm of tonsillar fossa. 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 - tonsils.

For Medicare Advantage risk adjustment, C09.0 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

ICD-10-CM Code
C09.0
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neoplasm of tonsillar fossa
Short Description
Malignant neoplasm of tonsillar fossa
Same as the full description in the CMS dataset.
Parent Code
C09
Malignant neoplasm of tonsil

Code Classification

ChapterC00–D49Neoplasms
SectionC00-C14Malignant neoplasms of lip, oral cavity and pharynx
CategoryC09Malignant neoplasm of tonsil
This CodeC09.0Malignant neoplasm of tonsillar fossa

Medicare Risk Adjustment (HCC)Billing

C09.0 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.

CMS-HCC V28 Category (Payment Model)
HCC 21— Lymphoma and Other Cancers
Payment HCC · PY 2026 one of 463 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.671
community, non-dual, aged · ranges 0.493–0.739 across segments
Hierarchy
Superseded by HCC 17, HCC 18, HCC 19, and HCC 20
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
HCC 11
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 11 · ESRD (V21): HCC 11 · ESRD (V24): HCC 11
ESRD V21 weights: 0.076 dialysis, 0.284–0.298 functioning graft · ESRD V24 weights: 0.059 dialysis, 0.257–0.362 functioning graft
Part D (RxHCC)
Not mapped
C09.0 does not risk-adjust in the RxHCC prescription drug model

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.

  • Malignant neoplasm of tonsillar fossa
  • Neoplasm of tonsillar fossa
  • Primary malignant neoplasm of lateral wall of oropharynx
  • Primary malignant neoplasm of tonsillar fossa
  • Primary squamous cell carcinoma of lateral wall of oropharynx
  • Primary squamous cell carcinoma of tonsillar fossa
  • Squamous cell carcinoma of lateral wall of oropharynx

Clinical ClassificationClinical

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

CCSR NEO009
Head and neck cancers - tonsils
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.
fossa (of) › tonsillarC09.0C79.89D00.08D10.5D37.05D49.0
glossopharyngeal sulcusC09.0C79.89D00.08D10.5D37.05D49.0
tonsillar fossaC09.0C79.89D00.08D10.5D37.05D49.0

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 C09.0 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
146.1 Mal neo tonsillar fossa
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 C09.0Overview

What is the ICD-10 code for malignant neoplasm of tonsillar fossa?

The ICD-10-CM code for malignant neoplasm of tonsillar fossa is C09.0 (sometimes written as C090). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Is C09.0 (Malignant neoplasm of tonsil) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report malignant neoplasm of tonsillar fossa on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C09.0 group to?

When malignant neoplasm of tonsillar fossa 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 C09.0?

Under the General Equivalence Mappings, malignant neoplasm of tonsillar fossa converts to ICD-9-CM 146.1 (mal neo tonsillar fossa). The mapping is a direct match.

What HCC is C09.0?

C09.0 (malignant neoplasm of tonsillar fossa) 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 C09.0 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, C09.0 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.