C18.8
BillableMalignant neoplasm of overlapping sites of colon
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C18.8 an HCC code?
Yes. C18.8 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 C18.8
For C18.8 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 C18.8 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C18.8 is the ICD-10-CM diagnosis code for malignant neoplasm of overlapping sites of colon. Cancer of the colon that involves multiple overlapping sections or sites within the colon rather than being confined to a single segment. C18.8 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, C18.8 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, C18.8 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.
Use this code only when the tumor clearly involves two or more distinct colon segments. Because C18.8 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 C18.8 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the tumor clearly involves two or more distinct colon segments
- •Document which specific segments are involved to support medical necessity and treatment planning
Clinical Significance
Overlapping sites of the colon indicates a malignant tumor that spans multiple colonic segments, typically reflecting larger, more advanced tumors. These patients often require more extensive surgical resection (subtotal or total colectomy) and may have a worse prognosis than single-segment disease. Accurate use of this code versus single-site or unspecified codes is important for both risk adjustment and surgical planning documentation.
Documentation Requirements
- ✓Documentation confirming the tumor involves two or more distinct segments of the colon
- ✓Identification of which specific segments are involved
- ✓Histological type and grade
- ✓Stage of disease with tumor dimensions
- ✓Surgical extent of resection
Commonly Confused Codes
- •C18.9 — Colon, unspecified: C18.8 is for known multi-segment disease; C18.9 is for unknown location — critical distinction
- •C18.0-C18.7 — Specific colon segments: use site-specific codes when tumor is confined to one segment
- •C21.8 — Overlapping sites of rectum, anus, and anal canal: different anatomical region