What is ICD-10 code C18.0?

C18.0 is the ICD-10-CM diagnosis code for Malignant neoplasm of cecum. Cancer that starts in the cecum, which is the pouch-like beginning of the large intestine where the small intestine connects. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C18.0 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C18.0 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. C18.0 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. C18.0 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 C18.0 map to under V28?

C18.0 maps to CMS-HCC V28 HCC 22 (Bladder, Colorectal, and Other Cancers). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM C18.0: Malignant neoplasm of cecum

C18.0 maps to CMS-HCC V28 22. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC18.0Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of digestive organs (C15-C26)

C18.0

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

Malignant neoplasm of cecum

Cancer that starts in the cecum, which is the pouch-like beginning of the large intestine where the small intestine connects.

Buddy Insight

Malignant neoplasm of the cecum is one of the most common colorectal cancer locations, as the cecum is where the small intestine connects to the large intestine.

CMS-HCC V28

Mapped

HCC 22

Bladder, Colorectal, and Othe...

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 011

HHS-HCC 011 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 11

Colorectal/Bladder/and Other ...

Code-level coefficient reference

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

C18Malignant neoplasm of colon

C18.0Malignant neoplasm of cecum

Inclusion Terms

Official

Malignant neoplasm of ileocecal valve

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C18.0 in this effective period.

Related Child Codes

Official

C18.1Malignant neoplasm of appendix

C18.2Malignant neoplasm of ascending colon

C18.3Malignant neoplasm of hepatic flexure

C18.4Malignant neoplasm of transverse colon

C18.5Malignant neoplasm of splenic flexure

Includes

Official

ICD-10-CM does not list Includes notes for C18.0 in this effective period.

Excludes 1

Official

malignant carcinoid tumors of the colon (C7A.02-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C18.0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C18.0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C18.0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation confirming cecum as the primary tumor location

Histological type and grade (adenocarcinoma is most common)

Stage of disease including depth of invasion and lymph node status

Microsatellite instability or mismatch repair status if tested

MEAT Support

HCC Buddy guidance

Documentation confirming cecum as the primary tumor location

Histological type and grade (adenocarcinoma is most common)

Stage of disease including depth of invasion and lymph node status

Microsatellite instability or mismatch repair status if tested

Audit Caution

HCC Buddy guidance

Confusing cecum with ascending colon — the cecum is the blind-ended pouch below the ileocecal valve

Coding ileocecal junction tumors without determining the primary site (ileum vs cecum)

Using C18.9 (unspecified colon) when colonoscopy clearly identifies the cecum

Missing that right-sided cancers (including cecum) have different molecular profiles that may affect treatment

Common Mistakes

HCC Buddy guidance

C18.2 — Ascending colon: the cecum is the initial pouch; the ascending colon begins above the ileocecal valve and runs superiorly

C17.2 — Ileum: the terminal ileum connects to the cecum; ensure the primary tumor is in the cecum, not the ileum

C18.1 — Appendix: the appendix arises from the cecum; appendiceal tumors have a separate code

C18.9 — Colon, unspecified: use C18.0 when cecum is documented

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 C18.0 an HCC code?

Yes. C18.0 (Malignant neoplasm of cecum) maps to HCC 22, Bladder, Colorectal, and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.363. 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: C18.0 is billable and maps to V28 HCC 22, Bladder, Colorectal, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C18.0
Description: Malignant neoplasm of cecum
HCC (V28): HCC 22 — Bladder, Colorectal, and Other Cancers
RAF reference coefficient: 0.363
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 22, Bladder, Colorectal, and Other Cancers

0.363

ESRDHCC 11, Colorectal/Bladder/and Other Cancers

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 C18.0 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for C18.0

For C18.0 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 C18.0 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C18.0 is the ICD-10-CM diagnosis code for malignant neoplasm of cecum. Cancer that starts in the cecum, which is the pouch-like beginning of the large intestine where the small intestine connects. C18.0 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of digestive organs (c15-c26).

Under the CMS-HCC V28 risk adjustment model, C18.0 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a source-labeled community, non-dual, aged reference coefficient of 0.363. No V24 mapping is shown for C18.0; use the applicable model and payment year when reviewing the V28 mapping. 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. 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.

Cecal cancers often present late; document stage and histological type for complete coding. Because C18.0 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 C18.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Cecal cancers often present late; document stage and histological type for complete coding
•Distinguish from ascending colon cancer; the cecum is the first part of the colon

Clinical Significance

Malignant neoplasm of the cecum is one of the most common colorectal cancer locations, as the cecum is where the small intestine connects to the large intestine. Cecal cancers are classified as right-sided colon cancers, which have distinct molecular features and clinical behavior compared to left-sided cancers. These tumors often present with iron deficiency anemia and occult blood loss rather than overt obstruction, leading to later-stage diagnosis.

Documentation Requirements

✓Documentation confirming cecum as the primary tumor location
✓Histological type and grade (adenocarcinoma is most common)
✓Stage of disease including depth of invasion and lymph node status
✓Microsatellite instability or mismatch repair status if tested
✓Colonoscopy or surgical confirmation of location

Commonly Confused Codes

•C18.2: Ascending colon: the cecum is the initial pouch; the ascending colon begins above the ileocecal valve and runs superiorly
•C17.2: Ileum: the terminal ileum connects to the cecum; ensure the primary tumor is in the cecum, not the ileum
•C18.1: Appendix: the appendix arises from the cecum; appendiceal tumors have a separate code
•C18.9: Colon, unspecified: use C18.0 when cecum is documented