C26.9
BillableMalignant neoplasm of ill-defined sites within the digestive system
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C26.9 an HCC code?
Yes. C26.9 maps to Colorectal, Bladder, and Other Cancers under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for C26.9
For C26.9to 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.
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 Colorectal, Bladder, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.000. Under the older V24 model, C26.9 mapped to the same category but with a base RAF weight of 0.306 — V28 recalibrated weights across the entire model. 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
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