What is ICD-10 code C26.9?

C26.9 is the ICD-10-CM diagnosis code for Malignant neoplasm of ill-defined sites within the digestive system. Cancer of the digestive system where the specific organ or site cannot be clearly identified or defined. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C26.9 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C26.9 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. C26.9 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. C26.9 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 C26.9 map to under V28?

C26.9 maps to CMS-HCC V28 22 (Bladder, Colorectal, and Other Cancers). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does C26.9 pay in RAF?

C26.9 carries a community, non-dual, aged (CNA) RAF weight of 0.363 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for C26.9?

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 C26.9, 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 documentation supports C26.9?

This is a catch-all code for ill-defined digestive cancers; use only when more specific site coding is impossible Document all available information about the tumor location to support medical necessity Because C26.9 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. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM C26.9: Malignant neoplasm

C26.9 maps to CMS-HCC V28 22 (RAF 0.363). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC coding software

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Code lookupC26.9Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C26.9

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

Malignant neoplasm of ill-defined sites within the digestive system

Cancer of the digestive system where the specific organ or site cannot be clearly identified or defined.

Buddy Insight

This is the least specific code for digestive system malignancies, used when the exact organ or site within the digestive system cannot be identified.

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

C26Malignant neoplasm of other and ill-defined digestive organs

C26.9Malignant neoplasm of ill-defined sites within the digestive system

Inclusion Terms

Official

Malignant neoplasm of alimentary canal or tract NOS
Malignant neoplasm of gastrointestinal tract NOS

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C26.9 in this effective period.

Related Child Codes

Official

C26.0Malignant neoplasm of intestinal tract, part unspecified

C26.1Malignant neoplasm of spleen

Includes

Official

ICD-10-CM does not list Includes notes for C26.9 in this effective period.

Excludes 1

Official

malignant neoplasm of abdominal NOS (C76.2)
malignant neoplasm of intra-abdominal NOS (C76.2)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C26.9 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C26.9 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C26.9 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology or clinical confirmation of digestive system malignancy

Documentation that all available diagnostic workup has been reviewed

Evidence of provider query for more specific anatomical location

Reason the specific site cannot be determined (e.g., unknown primary, extensive disease)

MEAT Support

HCC Buddy guidance

Pathology or clinical confirmation of digestive system malignancy

Documentation that all available diagnostic workup has been reviewed

Evidence of provider query for more specific anatomical location

Reason the specific site cannot be determined (e.g., unknown primary, extensive disease)

Audit Caution

HCC Buddy guidance

Using this as a convenience code when more specific digestive site information is available in the record

Not reviewing pathology, imaging, and endoscopy reports that may provide site specificity

Confusing ill-defined primary with metastatic disease involving the digestive tract

Failing to query providers for additional diagnostic information that could improve specificity

Common Mistakes

HCC Buddy guidance

C26.0 — Intestinal tract, part unspecified: More specific than C26.9 if the tumor is known to be intestinal

C80.1 — Malignant (primary) neoplasm, unspecified: Use when even the body system cannot be determined

C76.2 — Malignant neoplasm of abdomen: Use for ill-defined abdominal primary, not specifically digestive

C78.4-C78.89 — Secondary neoplasm codes: Ensure this is a primary neoplasm, not metastatic disease to the digestive system

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 C26.9 an HCC code?

Yes. C26.9 (Malignant neoplasm of ill-defined sites within the digestive system) 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: C26.9 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: C26.9
Description: Malignant neoplasm of ill-defined sites within the digestive system
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 C26.9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C26.9

For C26.9 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 C26.9 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C26.9 is the ICD-10-CM diagnosis code for malignant neoplasm of ill-defined sites within the digestive system. Cancer of the digestive system where the specific organ or site cannot be clearly identified or defined. C26.9 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, C26.9 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, C26.9 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.

This is a catch-all code for ill-defined digestive cancers; use only when more specific site coding is impossible. Because C26.9 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 C26.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This is a catch-all code for ill-defined digestive cancers; use only when more specific site coding is impossible
•Document all available information about the tumor location to support medical necessity

Clinical Significance

This is the least specific code for digestive system malignancies, used when the exact organ or site within the digestive system cannot be identified. It typically reflects incomplete documentation or unresolved diagnostic workups. While it still captures HCC risk, it is highly susceptible to audit challenges and should only be used as a last resort.

Documentation Requirements

✓Pathology or clinical confirmation of digestive system malignancy
✓Documentation that all available diagnostic workup has been reviewed
✓Evidence of provider query for more specific anatomical location
✓Reason the specific site cannot be determined (e.g., unknown primary, extensive disease)
✓Current treatment approach and disease status

Excludes 1, Do NOT code together

malignant neoplasm of abdominal NOS (C76.2)
malignant neoplasm of intra-abdominal NOS (C76.2)

Commonly Confused Codes

•C26.0: Intestinal tract, part unspecified: More specific than C26.9 if the tumor is known to be intestinal
•C80.1: Malignant (primary) neoplasm, unspecified: Use when even the body system cannot be determined
•C76.2: Malignant neoplasm of abdomen: Use for ill-defined abdominal primary, not specifically digestive
•C78.4-C78.89: Secondary neoplasm codes: Ensure this is a primary neoplasm, not metastatic disease to the digestive system