What is ICD-10 code C31.0?

C31.0 is the ICD-10-CM diagnosis code for Malignant neoplasm of maxillary sinus. Cancer that develops in the maxillary sinus, the large air-filled cavity in the cheekbone above the teeth. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C31.0 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C31.0 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. C31.0 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. C31.0 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 C31.0 map to under V28?

C31.0 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 C31.0 pay in RAF?

C31.0 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 C31.0?

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 C31.0, 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 C31.0: Malignant neoplasm

C31.0 maps to CMS-HCC V28 21 (RAF 0.671). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC Buddy coding tools

ICD-10-CM Code View

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Code lookupC31.0Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of respiratory and intrathoracic organs (C30-C39)

C31.0

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

Malignant neoplasm of maxillary sinus

Cancer that develops in the maxillary sinus, the large air-filled cavity in the cheekbone above the teeth.

Buddy Insight

Maxillary sinus cancer is the most common paranasal sinus malignancy, often presenting at advanced stages because early symptoms mimic sinusitis.

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

Mapped

HCC 22

Cancer, Other Specified Sites

RAF 0.124

Code Book Path

Official

C31Malignant neoplasm of accessory sinuses

C31.0Malignant neoplasm of maxillary sinus

Inclusion Terms

Official

Malignant neoplasm of antrum (Highmore) (maxillary)

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C31.0 in this effective period.

Related Child Codes

Official

C31.1Malignant neoplasm of ethmoidal sinus

C31.2Malignant neoplasm of frontal sinus

C31.3Malignant neoplasm of sphenoid sinus

C31.8Malignant neoplasm of overlapping sites of accessory sinuses

C31.9Malignant neoplasm of accessory sinus, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for C31.0 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C31.0 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C31.0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C31.0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C31.0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirmation with histological type (squamous cell most common, adenoid cystic, mucosal melanoma)

Imaging documenting extent of disease and invasion of adjacent structures (orbit, palate, infratemporal fossa)

TNM staging specific to maxillary sinus (Ohngren line relevant for prognosis)

Treatment plan including surgical approach and radiation therapy

MEAT Support

HCC Buddy guidance

Pathology confirmation with histological type (squamous cell most common, adenoid cystic, mucosal melanoma)

Imaging documenting extent of disease and invasion of adjacent structures (orbit, palate, infratemporal fossa)

TNM staging specific to maxillary sinus (Ohngren line relevant for prognosis)

Treatment plan including surgical approach and radiation therapy

Audit Caution

HCC Buddy guidance

Coding maxillary sinus cancer as nasal cavity cancer when the tumor extends into the nose — code the primary origin

Confusing maxillary sinus tumors with dental or oral cavity tumors when the hard palate is involved

Not distinguishing between different paranasal sinus sites which each have specific codes

Missing additional codes for orbital or skull base invasion when documented

Common Mistakes

HCC Buddy guidance

C31.1 — Ethmoidal sinus cancer: Adjacent sinus; ensure documentation specifies the maxillary sinus

C30.0 — Nasal cavity cancer: Maxillary sinus tumors may extend into the nasal cavity — code the primary site

C03.0-C03.1 — Malignant neoplasm of upper gum: Floor of maxillary sinus is the palate; oral cavity cancers are coded differently

J32.0 — Chronic maxillary sinusitis: Chronic sinusitis symptoms can mask underlying malignancy

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 C31.0 an HCC code?

Yes. C31.0 (Malignant neoplasm of maxillary sinus) 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: C31.0 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: C31.0
Description: Malignant neoplasm of maxillary sinus
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

RxHCCHCC 22, Cancer, Other Specified Sites

0.124

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 C31.0 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C31.0

For C31.0 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 C31.0 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C31.0 is the ICD-10-CM diagnosis code for malignant neoplasm of maxillary sinus. Cancer that develops in the maxillary sinus, the large air-filled cavity in the cheekbone above the teeth. C31.0 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of respiratory and intrathoracic organs (c30-c39).

Under the CMS-HCC V28 risk adjustment model, C31.0 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, C31.0 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.

Maxillary sinus cancer often presents late; document extent of invasion into adjacent structures. Because C31.0 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 C31.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Maxillary sinus cancer often presents late; document extent of invasion into adjacent structures
•Distinguish from other paranasal sinus cancers and ensure correct sinus site is coded

Clinical Significance

Maxillary sinus cancer is the most common paranasal sinus malignancy, often presenting at advanced stages because early symptoms mimic sinusitis. Treatment typically requires radical surgery (maxillectomy) with adjuvant radiation, resulting in high healthcare resource utilization. Accurate coding supports appropriate risk adjustment for these complex patients.

Documentation Requirements

✓Pathology confirmation with histological type (squamous cell most common, adenoid cystic, mucosal melanoma)
✓Imaging documenting extent of disease and invasion of adjacent structures (orbit, palate, infratemporal fossa)
✓TNM staging specific to maxillary sinus (Ohngren line relevant for prognosis)
✓Treatment plan including surgical approach and radiation therapy
✓Clear documentation distinguishing maxillary sinus from other paranasal sinuses

Commonly Confused Codes

•C31.1: Ethmoidal sinus cancer: Adjacent sinus; ensure documentation specifies the maxillary sinus
•C30.0: Nasal cavity cancer: Maxillary sinus tumors may extend into the nasal cavity: code the primary site
•C03.0-C03.1: Malignant neoplasm of upper gum: Floor of maxillary sinus is the palate; oral cavity cancers are coded differently
•J32.0: Chronic maxillary sinusitis: Chronic sinusitis symptoms can mask underlying malignancy