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

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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.

CMS-HCC V28

HCC 21

RAF 0.671

CMS-HCC V24

HCC 11

RAF 0.307

ACA/HHS

HCC 11

Varies by metal level

ESRD/PACE

HCC 11

RAF 0.059

RXHCC

HCC 22

RAF 0.124

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

ICD-10-CM does not list Excludes 2 notes for C01 in this effective period.

Related Child Codes

Official

ICD-10-CM does not list child codes under C01 for this display context.

Includes

Official

ICD-10-CM does not list Includes notes for C01 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C01 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C01 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 C01 in this effective period.

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

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is C01 an HCC code?

Yes. C01 maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24).

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 C01 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C01

For C01to 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 C01 during that encounter, not just copy-forwarded from a problem list.

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 community, non-dual, aged base RAF weight of 0.671. Under the older CMS-HCC V24 model, C01 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.

Base of tongue cancers are often squamous cell carcinomas; verify histology in documentation. Because C01 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 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

Because C01 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.

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.

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