C66.1
BillableMalignant neoplasm of right ureter
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C66.1 an HCC code?
Yes. C66.1 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 C66.1
For C66.1to 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 C66.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C66.1 is the ICD-10-CM diagnosis code for malignant neoplasm of right ureter. This code represents cancer that has developed in the right ureter, which is the tube that carries urine from the right kidney to the bladder. It is a malignant (cancerous) tumor that requires treatment. C66.1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of urinary tract (c64-c68).
Under the CMS-HCC V28 risk adjustment model, C66.1 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, C66.1 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.
Ensure laterality is documented in the medical record as 'right' to support the use of this specific code; do not use this code for left ureter (C66.2) or unspecified side (C66.9). Because C66.1 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 C66.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure laterality is documented in the medical record as 'right' to support the use of this specific code; do not use this code for left ureter (C66.2) or unspecified side (C66.9)
- •This code should be used as the primary diagnosis for cancer cases; pair with additional codes for histology type, stage, and any metastases as documented by the physician
Clinical Significance
Right ureteral cancer is an upper tract urothelial carcinoma arising from the tube connecting the kidney to the bladder. Like renal pelvis urothelial cancer, it carries significant risk for metachronous bladder cancer. Ureteral tumors are less common than renal pelvis or bladder cancers but share the same urothelial biology and require similar surveillance protocols.
Documentation Requirements
- ✓Pathology confirming right ureteral malignancy
- ✓Histologic type (urothelial carcinoma expected in most cases)
- ✓Location within the ureter (proximal, mid, or distal third)
- ✓Staging and grade
- ✓Hydronephrosis status
- ✓Treatment plan (nephroureterectomy with bladder cuff excision is standard)
Commonly Confused Codes
- •C65.1 — Right renal pelvis cancer; ureter and renal pelvis are contiguous but coded separately
- •C66.2 — Left ureter cancer; verify laterality
- •C66.9 — Unspecified ureter; use C66.1 when right is documented
- •C67.5 — Bladder neck cancer; distal ureteral tumors near the ureteral orifice may be confused with bladder tumors
- •N13.1 — Hydronephrosis with ureteral stricture; ureteral obstruction from cancer, not a separate code for the obstruction