C49.A4
BillableGastrointestinal stromal tumor of large intestine
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C49.A4 an HCC code?
Yes. C49.A4 maps to Melanoma and Other Skin Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma 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 C49.A4
For C49.A4 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 C49.A4 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C49.A4 is the ICD-10-CM diagnosis code for gastrointestinal stromal tumor of large intestine. A gastrointestinal stromal tumor that develops in the large intestine (colon), the final part of the digestive system. C49.A4 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of mesothelial and soft tissue (c45-c49).
Under the CMS-HCC V28 risk adjustment model, C49.A4 maps to Melanoma and Other Skin Cancers (HCC 23) with a community, non-dual, aged base RAF weight of 0.251. Under the older CMS-HCC V24 model, C49.A4 maps to Lymphoma and Other Cancers (HCC 10) with a community, non-dual, aged base RAF weight of 0.675. 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.
Distinguish between GIST of the colon and adenocarcinoma or other colon cancers. Because C49.A4 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 C49.A4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Distinguish between GIST of the colon and adenocarcinoma or other colon cancers
- •Document the specific segment of colon involved if available (ascending, transverse, descending, sigmoid)
Clinical Significance
Gastrointestinal stromal tumor of the large intestine (colon) is uncommon, accounting for approximately 1-2% of all GISTs. Colonic GISTs must be carefully distinguished from the far more common colonic adenocarcinoma, as the treatment approach (targeted therapy with imatinib for GIST versus chemotherapy for adenocarcinoma) is fundamentally different.
Documentation Requirements
- ✓Pathology confirming GIST in the colon with immunohistochemistry (KIT/CD117, DOG1)
- ✓Specific segment of colon involved (ascending, transverse, descending, sigmoid)
- ✓Tumor size and mitotic rate
- ✓Distinction from colonic adenocarcinoma or other colonic malignancies on pathology
- ✓Mutation analysis and treatment plan (imatinib eligibility)