C18.5
BillableMalignant neoplasm of splenic flexure
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C18.5 an HCC code?
Yes. C18.5 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 C18.5
For C18.5 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 C18.5 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C18.5 is the ICD-10-CM diagnosis code for malignant neoplasm of splenic flexure. Cancer that develops at the splenic flexure, which is the bend in the colon near the spleen where the transverse colon turns downward. C18.5 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, C18.5 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, C18.5 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.
The splenic flexure is a specific anatomical landmark; confirm documentation specifies this location rather than adjacent colon segments. Because C18.5 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 C18.5 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •The splenic flexure is a specific anatomical landmark; confirm documentation specifies this location rather than adjacent colon segments
- •This location may require different surgical approaches than other colon cancers
Clinical Significance
Malignant neoplasm of the splenic flexure occurs at the bend where the transverse colon turns downward to become the descending colon, near the spleen. This is one of the less common colorectal cancer sites and has unique surgical considerations due to its proximity to the spleen, left kidney, and pancreatic tail. Splenic flexure cancers may require mobilization of the spleen and distal pancreas during resection.
Documentation Requirements
- ✓Documentation specifying splenic flexure as the tumor location
- ✓Histological type and grade
- ✓Stage of disease
- ✓Relationship to spleen and adjacent structures
- ✓Colonoscopy or surgical confirmation
Commonly Confused Codes
- •C18.4 — Transverse colon: the splenic flexure is the bend at the end of the transverse colon, not the straight transverse segment
- •C18.6 — Descending colon: the descending colon begins after the splenic flexure going downward
- •C18.8 — Overlapping sites: use when tumor spans from transverse colon through splenic flexure into descending colon