C18.4
BillableMalignant neoplasm of transverse colon
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C18.4 an HCC code?
Yes. C18.4 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 C18.4
For C18.4 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 C18.4 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C18.4 is the ICD-10-CM diagnosis code for malignant neoplasm of transverse colon. Cancer that starts in the transverse colon, which is the part of the large intestine that runs horizontally across the upper abdomen. C18.4 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, C18.4 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, C18.4 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.
Verify the exact anatomical location is documented as transverse colon to distinguish from other colon segments. Because C18.4 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 C18.4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the exact anatomical location is documented as transverse colon to distinguish from other colon segments
- •Ensure histological type and stage are documented separately, as they are not included in this code
Clinical Significance
Malignant neoplasm of the transverse colon occurs in the horizontal segment of the large intestine that crosses the upper abdomen. The transverse colon represents a transitional zone between right-sided and left-sided colon cancers, and its molecular profile may have features of either. This location requires specific surgical planning, often involving extended colectomy to ensure adequate lymph node harvest and clear margins.
Documentation Requirements
- ✓Documentation confirming transverse colon as the tumor location
- ✓Histological type and grade
- ✓Stage of disease
- ✓Whether the tumor is in the proximal, mid, or distal transverse colon (affects surgical approach)
- ✓Colonoscopy or imaging confirmation
Commonly Confused Codes
- •C18.3 — Hepatic flexure: the proximal end of the transverse colon starts after the hepatic flexure
- •C18.5 — Splenic flexure: the distal end of the transverse colon transitions to the splenic flexure
- •C18.8 — Overlapping sites: use when the tumor clearly spans the transverse colon into an adjacent segment