Skip to content
HCC Buddy home

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

C09.0 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC09.0

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

C09.0

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

Malignant neoplasm of tonsillar fossa

Cancer that develops in the tonsillar fossa, which is the pocket-like area where the tonsil sits in the throat.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of the tonsillar fossa is one of the most common oropharyngeal cancers, with increasing incidence due to human papillomavirus (HPV) infection.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 21

Coefficient HCC 21: 0.671 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 011

Code-level coefficient reference

ESRD/PACE

HCC 11

Code-level coefficient reference

RXHCC

N/A

—

Not mapped

Code Book Path

Official
C09Malignant neoplasm of tonsilC09.0Malignant neoplasm of tonsillar fossa

Inclusion Terms

Official

No inclusion terms are included in this display for C09.0. Check the code and parent instructions in the Code Book.

Excludes 2

Official
  • malignant neoplasm of lingual tonsil (C02.4)Inherited from C09
  • malignant neoplasm of pharyngeal tonsil (C11.1)Inherited from C09

Related Codes

Official
C09.1Malignant neoplasm of tonsillar pillar (anterior) (posterior)C09.8Malignant neoplasm of overlapping sites of tonsilC09.9Malignant neoplasm of tonsil, unspecified

Includes

Official

No Includes notes are included in this display for C09.0. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for C09.0. Check the code and parent instructions in the Code Book.

Code First

Official

No Code First sequencing instructions are included in this display for C09.0. Check the code and parent instructions in the Code Book.

Use Additional

Official
  • code to identify:Inherited from C09
  • alcohol abuse and dependence (F10.-)Inherited from C09
  • exposure to environmental tobacco smoke (Z77.22)Inherited from C09
  • exposure to tobacco smoke in the perinatal period (P96.81)Inherited from C09
  • history of tobacco dependence (Z87.891)Inherited from C09
  • occupational exposure to environmental tobacco smoke (Z57.31)Inherited from C09
  • tobacco dependence (F17.-)Inherited from C09
  • tobacco use (Z72.0)Inherited from C09

Code Also

Official

No Code Also instructions are included in this display for C09.0. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Pathology-confirmed malignancy with histological type
HPV/p16 status documented (critical for prognosis and treatment decisions)
Specific documentation of tonsillar fossa as primary site
Laterality (right or left tonsillar fossa)

MEAT Support

HCC Buddy guidance
Pathology-confirmed malignancy with histological type
HPV/p16 status documented (critical for prognosis and treatment decisions)
Specific documentation of tonsillar fossa as primary site
Laterality (right or left tonsillar fossa)

Audit Caution

HCC Buddy guidance
Failing to document HPV/p16 status which fundamentally changes staging and prognosis
Confusing tonsillar fossa (the pocket containing the tonsil) with tonsillar pillar (the tissue arches surrounding the fossa)
Using unspecified tonsil code C09.9 when documentation clearly specifies the fossa
Not capturing laterality — tonsillar cancers are almost always unilateral and laterality is always identifiable

Common Mistakes

HCC Buddy guidance
C09.1 — Tonsillar pillar; the fossa is the pocket where the tonsil sits, the pillars are the tissue folds flanking the tonsil
C09.9 — Tonsil, unspecified; avoid when fossa is specifically documented
C09.8 — Overlapping sites of tonsil; use when tumor spans multiple tonsillar subsites
C10.2 — Lateral wall of oropharynx; tonsillar fossa tumors may extend to the lateral oropharyngeal wall

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 C09.0 an HCC code?

Yes. C09.0 (Malignant neoplasm of tonsillar fossa) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C09.0 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
C09.0
Description
Malignant neoplasm of tonsillar fossa
HCC (V28)
HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient
0.671
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers
0.671
ESRDHCC 11, Colorectal/Bladder/and Other Cancers
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C09.0 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C09.0

For C09.0, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

  • 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

Coder workflow notes

Get the V28 mapping + MEAT cheat sheet

One printable reference: check representative V28 mappings and the documentation reminders your note needs. Free, no card.

Free PDF. No card. Unsubscribe anytime.

What This Code Means

C09.0 is the ICD-10-CM diagnosis code for malignant neoplasm of tonsillar fossa. Cancer that develops in the tonsillar fossa, which is the pocket-like area where the tonsil sits in the throat. C09.0 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, C09.0 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. No V24 mapping is shown for C09.0; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Confirm tonsillar fossa location is documented to distinguish from tonsillar pillar cancers. For C09.0, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, and MEAT documentation criteria for C09.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Confirm tonsillar fossa location is documented to distinguish from tonsillar pillar cancers
  • •Document laterality (left or right) when specified

Clinical Significance

Malignant neoplasm of the tonsillar fossa is one of the most common oropharyngeal cancers, with increasing incidence due to human papillomavirus (HPV) infection. HPV-positive tonsillar cancers have a markedly better prognosis than HPV-negative tumors, making HPV status documentation critical for accurate prognostication and treatment planning.

Documentation Requirements

  • ✓Pathology-confirmed malignancy with histological type
  • ✓HPV/p16 status documented (critical for prognosis and treatment decisions)
  • ✓Specific documentation of tonsillar fossa as primary site
  • ✓Laterality (right or left tonsillar fossa)
  • ✓TNM staging using the appropriate staging system (AJCC 8th edition separates HPV-positive and HPV-negative oropharyngeal cancer staging)

Commonly Confused Codes

  • •C09.1: Tonsillar pillar; the fossa is the pocket where the tonsil sits, the pillars are the tissue folds flanking the tonsil
  • •C09.9: Tonsil, unspecified; avoid when fossa is specifically documented
  • •C09.8: Overlapping sites of tonsil; use when tumor spans multiple tonsillar subsites
  • •C10.2: Lateral wall of oropharynx; tonsillar fossa tumors may extend to the lateral oropharyngeal wall

Child Codes

C09.0Malignant neoplasm of tonsillar fossa
HCC 21
C09.1Malignant neoplasm of tonsillar pillar (anterior) (posterior)
HCC 21
C09.8Malignant neoplasm of overlapping sites of tonsil
HCC 21
C09.9Malignant neoplasm of tonsil, unspecified
HCC 21

Code Hierarchy

└C09Malignant neoplasm of tonsil└C09.0Malignant neoplasm of tonsillar fossa
└C09.0Malignant neoplasm of tonsillar fossa

Also searched as

  • C09 0
  • C090

For C09.0, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

C09.0 maps to CMS-HCC V28 category 21, Lymphoma and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C09.0. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

Work C09.0 in HCC Buddy

Open C09.0 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

Open in Code BookOpen in EncoderStart Pro