What is ICD-10 code C03.1?

C03.1 is the ICD-10-CM diagnosis code for Malignant neoplasm of lower gum. Cancer that starts in the lower gum tissue, typically involving the tissue covering the lower jaw bone. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C03.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C03.1 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. C03.1 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. C03.1 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.

What is the V28 vs V24 difference for C03.1?

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 C03.1, 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.

What should coders know when reporting C03.1?

Verify laterality if documented (left vs right lower gum) Distinguish from upper gum (C03.0) and unspecified gum (C03.9) Because C03.1 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM C03.1: Malignant neoplasm of lower

ICD-10-CM Code View

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Code lookupC03.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C03.1

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

Malignant neoplasm of lower gum

Cancer that starts in the lower gum tissue, typically involving the tissue covering the lower jaw bone.

Buddy Insight

Malignant neoplasm of the lower gum involves cancer of the mandibular gingiva.

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

C03Malignant neoplasm of gum

C03.1Malignant neoplasm of lower gum

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C03.1 in this effective period.

Excludes 2

Official

malignant odontogenic neoplasms (C41.0-C41.1)

Related Child Codes

Official

C03.0Malignant neoplasm of upper gum

C03.9Malignant neoplasm of gum, unspecified

Includes

Official

malignant neoplasm of alveolar (ridge) mucosa
malignant neoplasm of gingiva

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C03.1 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C03.1 in this effective period.

Use Additional

Official

code to identify:
alcohol abuse and dependence (F10.-)
history of tobacco dependence (Z87.891)
tobacco dependence (F17.-)
tobacco use (Z72.0)

Code Also

Official

ICD-10-CM does not list Code Also instructions for C03.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology-confirmed malignancy with histological type (typically squamous cell carcinoma)

Specific site documented as lower gum or mandibular gingiva

TNM staging with depth of invasion, particularly bone involvement

Laterality if documented (left vs right mandibular gingiva)

MEAT Support

HCC Buddy guidance

Pathology-confirmed malignancy with histological type (typically squamous cell carcinoma)

Specific site documented as lower gum or mandibular gingiva

TNM staging with depth of invasion, particularly bone involvement

Laterality if documented (left vs right mandibular gingiva)

Audit Caution

HCC Buddy guidance

Confusing the lower gum (gingiva of mandible) with floor of mouth (C04.x) when tumor extends between these sites

Using C03.9 unspecified when the provider clearly documents 'lower gum' or 'mandibular gingiva'

Missing the need for an additional code for bone invasion (C41.1) when tumor has extended into mandible from gum origin

Not capturing current treatment status which affects whether to code active cancer vs personal history

Common Mistakes

HCC Buddy guidance

C03.0 — Malignant neoplasm of upper gum; ensure documentation specifies mandibular (lower) not maxillary (upper) gingiva

C03.9 — Malignant neoplasm of gum, unspecified; avoid when lower gum is clearly documented

C41.1 — Malignant neoplasm of mandible; use when cancer originates in bone rather than overlying gum tissue

C04.0 — Malignant neoplasm of anterior floor of mouth; adjacent site that may overlap with lower gum tumors

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 C03.1 an HCC code?

Yes. C03.1 (Malignant neoplasm of lower gum) 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: C03.1 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: C03.1
Description: Malignant neoplasm of lower gum
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 C03.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C03.1

For C03.1 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 C03.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C03.1 is the ICD-10-CM diagnosis code for malignant neoplasm of lower gum. Cancer that starts in the lower gum tissue, typically involving the tissue covering the lower jaw bone. C03.1 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, C03.1 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, C03.1 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.

Verify laterality if documented (left vs right lower gum). Because C03.1 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 C03.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify laterality if documented (left vs right lower gum)
•Distinguish from upper gum (C03.0) and unspecified gum (C03.9)

Clinical Significance

Malignant neoplasm of the lower gum involves cancer of the mandibular gingiva. Lower gum cancers are more common than upper gum cancers and frequently invade the mandibular bone, often requiring more extensive surgical intervention including mandibulectomy.

Documentation Requirements

✓Pathology-confirmed malignancy with histological type (typically squamous cell carcinoma)
✓Specific site documented as lower gum or mandibular gingiva
✓TNM staging with depth of invasion, particularly bone involvement
✓Laterality if documented (left vs right mandibular gingiva)
✓Treatment plan and current status (active, remission, or surveillance)

Commonly Confused Codes

•C03.0: Malignant neoplasm of upper gum; ensure documentation specifies mandibular (lower) not maxillary (upper) gingiva
•C03.9: Malignant neoplasm of gum, unspecified; avoid when lower gum is clearly documented
•C41.1: Malignant neoplasm of mandible; use when cancer originates in bone rather than overlying gum tissue
•C04.0: Malignant neoplasm of anterior floor of mouth; adjacent site that may overlap with lower gum tumors