What is ICD-10 code C09.1?

C09.1 is the ICD-10-CM diagnosis code for Malignant neoplasm of tonsillar pillar (anterior) (posterior). Cancer that starts in the tonsillar pillar, which is the fold of tissue on either side of the tonsil in the throat. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C09.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C09.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C09.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C09.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does C09.1 map to under V28?

C09.1 maps to CMS-HCC V28 21 (Lymphoma and Other Cancers). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does C09.1 pay in RAF?

C09.1 carries a community, non-dual, aged (CNA) RAF weight of 0.671 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for C09.1?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C09.1, V28 maps to Lymphoma and Other Cancers at RAF 0.671 while V24 mapped to Colorectal, Bladder, and Other Cancers at RAF 0.307. Both models can still appear in legacy data and in payer-specific lookback periods.

2026 ICD-10-CM C09.1: Malignant neoplasm

C09.1 maps to CMS-HCC V28 21 (RAF 0.671). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC Buddy coding tools

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Code lookupC09.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C09.1

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

Malignant neoplasm of tonsillar pillar (anterior) (posterior)

Cancer that starts in the tonsillar pillar, which is the fold of tissue on either side of the tonsil in the throat.

Buddy Insight

Malignant neoplasm of the tonsillar pillar involves cancer of the anterior or posterior faucial pillars, the mucosal folds that border the tonsillar fossa.

CMS-HCC V28

Mapped

HCC 21

Lymphoma and Other Cancers

RAF 0.671

CMS-HCC V24

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.307

ACA/HHS

Mapped

HCC 11

HHS-HCC 11

Varies by metal level

ESRD/PACE

Mapped

HCC 11

Colorectal, Bladder, and Othe...

RAF 0.059

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

C09Malignant neoplasm of tonsil

C09.1Malignant neoplasm of tonsillar pillar (anterior) (posterior)

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C09.1 in this effective period.

Excludes 2

Official

malignant neoplasm of lingual tonsil (C02.4)
malignant neoplasm of pharyngeal tonsil (C11.1)

Related Child Codes

Official

C09.0Malignant neoplasm of tonsillar fossa

C09.8Malignant neoplasm of overlapping sites of tonsil

C09.9Malignant neoplasm of tonsil, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for C09.1 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C09.1 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C09.1 in this effective period.

Use Additional

Official

code to identify:
alcohol abuse and dependence (F10.-)
exposure to environmental tobacco smoke (Z77.22)
exposure to tobacco smoke in the perinatal period (P96.81)
history of tobacco dependence (Z87.891)

Code Also

Official

ICD-10-CM does not list Code Also instructions for C09.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology-confirmed malignancy specifying tonsillar pillar origin

Specification of anterior vs posterior pillar if documented

HPV/p16 testing status

Laterality (left or right)

MEAT Support

HCC Buddy guidance

Pathology-confirmed malignancy specifying tonsillar pillar origin

Specification of anterior vs posterior pillar if documented

HPV/p16 testing status

Laterality (left or right)

Audit Caution

HCC Buddy guidance

Not distinguishing anterior pillar from posterior pillar when documentation specifies one

Using tonsillar fossa code (C09.0) when the cancer originates in the pillar tissue

Failing to assess extension to the soft palate from an anterior pillar tumor, which could change the code

Missing HPV/p16 documentation which is critical for all oropharyngeal squamous cell carcinomas

Common Mistakes

HCC Buddy guidance

C09.0 — Tonsillar fossa; the fossa is the pocket itself, the pillars are the surrounding tissue folds

C05.1 — Soft palate; the anterior tonsillar pillar merges with the soft palate superiorly

C09.8 — Overlapping sites of tonsil; use when cancer spans fossa and pillar

C10.2 — Lateral wall of oropharynx; pillar cancers may extend to the lateral pharyngeal 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 C09.1 an HCC code?

Yes. C09.1 (Malignant neoplasm of tonsillar pillar (anterior) (posterior)) maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24), with a community non-dual aged RAF of 0.671. It is billable for payment year 2026.

Coder answer: C09.1 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: C09.1
Description: Malignant neoplasm of tonsillar pillar (anterior) (posterior)
HCC (V28): HCC 21 — Lymphoma and Other Cancers
RAF: 0.671
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers

0.671

V24HCC 11, Colorectal, Bladder, and Other Cancers

0.307

ESRDHCC 11, Colorectal, Bladder, and Other Cancers

0.059

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work C09.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C09.1

For C09.1 to 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 C09.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C09.1 is the ICD-10-CM diagnosis code for malignant neoplasm of tonsillar pillar (anterior) (posterior). Cancer that starts in the tonsillar pillar, which is the fold of tissue on either side of the tonsil in the throat. C09.1 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, C09.1 maps to Lymphoma and Other Cancers (HCC 21) with a community, non-dual, aged base RAF weight of 0.671. Under the older CMS-HCC V24 model, C09.1 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.307. 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.

Specify anterior or posterior pillar involvement when documented. Because C09.1 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 C09.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Specify anterior or posterior pillar involvement when documented
•Distinguish from tonsillar fossa (C09.0) and other oropharyngeal sites

Clinical Significance

Malignant neoplasm of the tonsillar pillar involves cancer of the anterior or posterior faucial pillars, the mucosal folds that border the tonsillar fossa. Cancers of the tonsillar pillars may present differently from tonsillar fossa cancers and can extend to the soft palate or tongue base, requiring careful documentation of the extent of disease.

Documentation Requirements

✓Pathology-confirmed malignancy specifying tonsillar pillar origin
✓Specification of anterior vs posterior pillar if documented
✓HPV/p16 testing status
✓Laterality (left or right)
✓Assessment of extension to adjacent structures (soft palate, tongue base, tonsillar fossa)

Commonly Confused Codes

•C09.0: Tonsillar fossa; the fossa is the pocket itself, the pillars are the surrounding tissue folds
•C05.1: Soft palate; the anterior tonsillar pillar merges with the soft palate superiorly
•C09.8: Overlapping sites of tonsil; use when cancer spans fossa and pillar
•C10.2: Lateral wall of oropharynx; pillar cancers may extend to the lateral pharyngeal wall