C18.2
BillableMalignant neoplasm of ascending colon
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C18.2 an HCC code?
Yes. C18.2 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 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.
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 Colorectal, Bladder, and Other Cancers (HCC 22) with a community, non-dual, aged base RAF weight of 0.000. Under the older V24 model, C18.2 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.
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