C18.9 ICD-10-CM Code: Malignant neoplasm of colon, unspecified
C18.9 maps to CMS-HCC V28 22. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools
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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of digestive organs (C15-C26)
C18.9
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMalignant neoplasm of colon, unspecified
Cancer of the colon where the specific location within the colon is not specified or documented.
Buddy Insight
Unspecified colon cancer is used when documentation confirms malignancy in the colon but does not identify the specific segment.
CMS-HCC V28
MappedHCC 22
Coefficient HCC 22: 0.363 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 011
Code-level coefficient reference
ESRD/PACE
MappedHCC 11
Code-level coefficient reference
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
Official- Malignant neoplasm of large intestine NOS
Excludes 2
Official- gastrointestinal stromal tumors (C49.A-)Inherited from C15-C26
Related Codes
Includes
OfficialNo Includes notes are included in this display for C18.9. Check the code and parent instructions in the Code Book.
Excludes 1
Official- Kaposi's sarcoma of gastrointestinal sites (C46.4)Inherited from C15-C26, C18
- malignant carcinoid tumors of the colon (C7A.02-)Inherited from C15-C26, C18
Code First
OfficialNo Code First sequencing instructions are included in this display for C18.9. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for C18.9. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for C18.9. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 C18.9 an HCC code?
Yes. C18.9 (Malignant neoplasm of colon, unspecified) 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: C18.9 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
- C18.9
- Description
- Malignant neoplasm of colon, unspecified
- HCC (V28)
- HCC 22 — Bladder, Colorectal, and Other Cancers
- RAF reference coefficient
- 0.363
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 C18.9 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C18.9
For C18.9, 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
C18.9 is the ICD-10-CM diagnosis code for malignant neoplasm of colon, unspecified. Cancer of the colon where the specific location within the colon is not specified or documented. C18.9 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, C18.9 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a source-labeled community, non-dual, aged reference coefficient of 0.363. 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.
This is a less specific code; query the provider if the exact colon location can be determined from pathology or imaging reports. For C18.9, 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 C18.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a less specific code; query the provider if the exact colon location can be determined from pathology or imaging reports
- •Use only when the anatomical site cannot be determined from available documentation
Clinical Significance
Unspecified colon cancer is used when documentation confirms malignancy in the colon but does not identify the specific segment. This code represents a documentation improvement opportunity, as the anatomical location of colon cancer affects both treatment planning and prognostic assessment. Despite being unspecified, this diagnosis still maps to the same HCC as specified colon cancers, but lacks the audit defensibility of more specific codes.
Documentation Requirements
- ✓Confirmed malignancy of the colon
- ✓Review of colonoscopy, pathology, surgical, and imaging reports for segment identification before defaulting to unspecified
- ✓Histological type if known
- ✓Stage of disease
- ✓Treatment status
Commonly Confused Codes
- •C18.0-C18.7: Specific colon segments: always assign the most specific code available from documentation
- •C18.8: Overlapping sites: use when multi-segment involvement is confirmed, not when location is unknown
- •C19: Rectosigmoid junction: if the cancer involves the junction, use this more specific code
- •C26.0: Intestinal tract, part unspecified: even less specific; use C18.9 when colon is confirmed