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C01 ICD-10-CM Code: Malignant neoplasm of base of tongue

C01 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 · HCC Buddy coding tools

ICD-10-CM Code View

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Code lookupC01

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

C01

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

Malignant neoplasm of base of tongue

Cancer that develops at the base of the tongue, the area where the tongue connects to the throat.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of base of tongue is a serious cancer often associated with human papillomavirus (HPV) infection in younger patients and tobacco/alcohol use in older patients.

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

HCC 22

Code-level coefficient reference

Code Book Path

Official
C0Malignant neoplasms of lip, oral cavity and pharynx (C00-C14)C01Malignant neoplasm of base of tongue

Inclusion Terms

Official
  • Malignant neoplasm of dorsal surface of base of tongue
  • Malignant neoplasm of fixed part of tongue NOS
  • Malignant neoplasm of posterior third of tongue

Excludes 2

Official

No Excludes 2 notes are included in this display for C01. Check the code and parent instructions in the Code Book.

Related Codes

Official

No related codes are included in this display for C01. Check the Code Book for the complete code path.

Includes

Official

No Includes notes are included in this display for C01. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for C01. Check the code and parent instructions in the Code Book.

Code First

Official

No Code First sequencing instructions are included in this display for C01. Check the code and parent instructions in the Code Book.

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

No Code Also instructions are included in this display for C01. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Pathology report confirming malignancy with histologic type (squamous cell carcinoma most common)
Documentation specifying base of tongue as the primary tumor site
TNM staging documented (tumor size, nodal involvement, metastasis)
HPV/p16 status documented (prognostically significant)

MEAT Support

HCC Buddy guidance
Pathology report confirming malignancy with histologic type (squamous cell carcinoma most common)
Documentation specifying base of tongue as the primary tumor site
TNM staging documented (tumor size, nodal involvement, metastasis)
HPV/p16 status documented (prognostically significant)

Audit Caution

HCC Buddy guidance
Confusing base of tongue (posterior third, C01) with anterior tongue (C02 codes) — the base of tongue is part of the oropharynx and has different staging
Coding a historical cancer as active — verify with the provider whether the malignancy is current or in remission
Not checking for concurrent metastatic disease to lymph nodes (C77) or distant sites which require additional codes
Missing the HPV association, which while not changing the primary code, affects staging and prognosis documentation

Common Mistakes

HCC Buddy guidance
C02.4 (Malignant neoplasm of lingual tonsil) - lingual tonsil is distinct lymphoid tissue at the tongue base; verify exact site
C02.0 (Malignant neoplasm of dorsal surface of tongue) - dorsal surface is the anterior two-thirds; base is posterior third
C09.9 (Malignant neoplasm of tonsil, unspecified) - tonsillar cancer is a separate oropharyngeal site from tongue base
Z85.810 (Personal history of malignant neoplasm of tongue) - use for historical cancer that has been treated and is in remission

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 C01 an HCC code?

Yes. C01 (Malignant neoplasm of base of tongue) 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: C01 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
C01
Description
Malignant neoplasm of base of tongue
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
RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors
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 C01 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C01

For C01, 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

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What This Code Means

C01 is the ICD-10-CM diagnosis code for malignant neoplasm of base of tongue. Cancer that develops at the base of the tongue, the area where the tongue connects to the throat. C01 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, C01 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. 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.

Base of tongue cancers are often squamous cell carcinomas; verify histology in documentation. For C01, 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 C01 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Base of tongue cancers are often squamous cell carcinomas; verify histology in documentation
  • •Ensure this code is not confused with other tongue locations like dorsal or ventral surfaces

Clinical Significance

Malignant neoplasm of base of tongue is a serious cancer often associated with human papillomavirus (HPV) infection in younger patients and tobacco/alcohol use in older patients. Base of tongue cancers are typically diagnosed at advanced stages due to their posterior location and often present with cervical lymph node metastases. Accurate site-specific coding is essential as treatment and prognosis differ by anatomic subsite.

Documentation Requirements

  • ✓Pathology report confirming malignancy with histologic type (squamous cell carcinoma most common)
  • ✓Documentation specifying base of tongue as the primary tumor site
  • ✓TNM staging documented (tumor size, nodal involvement, metastasis)
  • ✓HPV/p16 status documented (prognostically significant)
  • ✓Treatment plan: surgery, radiation, chemotherapy, or combination
  • ✓Active vs historical cancer status clearly documented

Use Additional Code

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

Commonly Confused Codes

  • •C02.4 (Malignant neoplasm of lingual tonsil) - lingual tonsil is distinct lymphoid tissue at the tongue base; verify exact site
  • •C02.0 (Malignant neoplasm of dorsal surface of tongue) - dorsal surface is the anterior two-thirds; base is posterior third
  • •C09.9 (Malignant neoplasm of tonsil, unspecified) - tonsillar cancer is a separate oropharyngeal site from tongue base
  • •Z85.810 (Personal history of malignant neoplasm of tongue) - use for historical cancer that has been treated and is in remission

Code Hierarchy

└C01Malignant neoplasm of base of tongue
└C01Malignant neoplasm of base of tongue

For C01, 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.

C01 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 C01. 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.

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