What is ICD-10 code C18.2?

C18.2 is the ICD-10-CM diagnosis code for Malignant neoplasm of ascending colon. Cancer that develops in the ascending colon, which is the first vertical section of the large intestine on the right side of the abdomen. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C18.2 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C18.2 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. C18.2 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. C18.2 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 C18.2?

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 C18.2, V28 maps to Bladder, Colorectal, and Other Cancers at RAF 0.363 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 C18.2?

Right-sided colon cancers may present with different symptoms than left-sided lesions; document clinical presentation Verify histological type and stage; adenocarcinoma is the most common type Because C18.2 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 C18.2: Malignant neoplasm

ICD-10-CM Code View

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Code lookupC18.2Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C18.2

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

Malignant neoplasm of ascending colon

Cancer that develops in the ascending colon, which is the first vertical section of the large intestine on the right side of the abdomen.

Buddy Insight

Malignant neoplasm of the ascending colon is classified as a right-sided colon cancer, which has distinct clinical and molecular characteristics compared to left-sided colon cancer.

CMS-HCC V28

Mapped

HCC 22

Bladder, Colorectal, and Othe...

RAF 0.363

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

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

C18Malignant neoplasm of colon

C18.2Malignant neoplasm of ascending colon

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C18.2 in this effective period.

Excludes 2

Official

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

Related Child Codes

Official

C18.0Malignant neoplasm of cecum

C18.1Malignant neoplasm of appendix

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 C18.2 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 C18.2 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C18.2 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C18.2 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation confirming ascending colon as the tumor location

Histological type and grade

Stage of disease (TNM staging)

Microsatellite instability or mismatch repair status

MEAT Support

HCC Buddy guidance

Documentation confirming ascending colon as the tumor location

Histological type and grade

Stage of disease (TNM staging)

Microsatellite instability or mismatch repair status

Audit Caution

HCC Buddy guidance

Coding hepatic flexure cancer as ascending colon or vice versa — these are distinct anatomical sites

Using the unspecified colon code when colonoscopy or surgical pathology specifies ascending colon

Not recognizing that 'right hemicolectomy' implies ascending colon involvement but should be confirmed by pathology for exact site

Common Mistakes

HCC Buddy guidance

C18.0 — Cecum: the cecum is the blind pouch below the ileocecal valve; the ascending colon runs superiorly from the cecum

C18.3 — Hepatic flexure: the hepatic flexure is the turn at the top of the ascending colon; ensure tumor is in the straight ascending portion

C18.9 — Colon, unspecified: use C18.2 when ascending colon is specifically 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 C18.2 an HCC code?

Yes. C18.2 (Malignant neoplasm of ascending colon) maps to Bladder, Colorectal, 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 0.363. It is billable for payment year 2026.

Coder answer: C18.2 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: C18.2
Description: Malignant neoplasm of ascending colon
HCC (V28): HCC 22 — Bladder, Colorectal, and Other Cancers
RAF: 0.363
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 22, Bladder, Colorectal, and Other Cancers

0.363

V24HCC 11, Colorectal, Bladder, and Other Cancers

0.307

ESRDHCC 11, Colorectal, Bladder, and Other Cancers

0.059

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 C18.2 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C18.2

For C18.2 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 C18.2 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C18.2 is the ICD-10-CM diagnosis code for malignant neoplasm of ascending colon. Cancer that develops in the ascending colon, which is the first vertical section of the large intestine on the right side of the abdomen. C18.2 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, C18.2 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.363. Under the older CMS-HCC V24 model, C18.2 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.

Right-sided colon cancers may present with different symptoms than left-sided lesions; document clinical presentation. Because C18.2 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 C18.2 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Right-sided colon cancers may present with different symptoms than left-sided lesions; document clinical presentation
•Verify histological type and stage; adenocarcinoma is the most common type

Clinical Significance

Malignant neoplasm of the ascending colon is classified as a right-sided colon cancer, which has distinct clinical and molecular characteristics compared to left-sided colon cancer. Right-sided cancers tend to present later with anemia and weight loss rather than obstruction or bleeding, and they are more commonly associated with microsatellite instability. These distinctions affect treatment decisions, including the potential benefit of immunotherapy for microsatellite instability-high tumors.

Documentation Requirements

✓Documentation confirming ascending colon as the tumor location
✓Histological type and grade
✓Stage of disease (TNM staging)
✓Microsatellite instability or mismatch repair status
✓Colonoscopy or surgical documentation confirming the site

Commonly Confused Codes

•C18.0: Cecum: the cecum is the blind pouch below the ileocecal valve; the ascending colon runs superiorly from the cecum
•C18.3: Hepatic flexure: the hepatic flexure is the turn at the top of the ascending colon; ensure tumor is in the straight ascending portion
•C18.9: Colon, unspecified: use C18.2 when ascending colon is specifically documented