2027 ICD-10-CM Diagnosis Code C66.1Malignant neoplasm of right ureter
ICD-10-CM Codes›C00–D49›C64-C68›C66
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 22
- Chronic Condition
C66.1 is a billable ICD-10-CM diagnosis code for malignant neoplasm of right ureter. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 656 through 658, 686 through 688. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 23 closely related codes. Coders also document this condition as bilateral primary malignant neoplasm of ureters. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Urinary system cancers - ureter and renal pelvis.
For Medicare Advantage risk adjustment, C66.1 maps to CMS-HCC Category 22 (Bladder, Colorectal, and Other Cancers) under the V28 model, adding a risk factor of about 0.363 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C66.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Bilateral primary malignant neoplasm of ureters
- Primary malignant neoplasm of left ureter
- Primary malignant neoplasm of right ureter
- Primary transitional cell carcinoma of right ureter
- Primary transitional cell carcinoma of upper urinary tract
- Primary transitional cell carcinoma of ureter
- Transitional cell carcinoma of right ureter
- Transitional cell carcinoma of ureter
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to C66.1: its own notes plus those printed at C66 and Chapter 2. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Notes
General instructions on how these codes are used.
- Functional activity
- All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
- Morphology [Histology]
- Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
- Primary malignant neoplasms overlapping site boundaries
- A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous, such as tumors in different quadrants of the same breast, codes for each site should be assigned.
- Malignant neoplasm of ectopic tissue
- Malignant neoplasms of ectopic tissue are to be coded to the site mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name C66.1, its category, or a range that includes it.
Applicable To 2
These notes mention C66.1.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Malignant Ureter Neoplasm
a primary or metastatic malignant tumor involving the ureter. the majority are carcinomas.
Patient EducationClinical
Cancer
Cancer is not just one disease but many diseases. Cancer begins in your cells, which are the building blocks of your body. Usually, your body forms new cells as needed, replacing old cells that die. Sometimes this process goes wrong. New cells grow even when you don't need them, and old cells don't die when they should.
The full article covers:
- What is cancer?
- What are the types of cancer?
- How does cancer develop?
- What are the symptoms of cancer?
- How is cancer diagnosed?
- What are the treatments for cancer?
- Can cancer be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert C66.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C66.1Overview
What is the ICD-10 code for malignant neoplasm of right ureter?
The ICD-10-CM code for malignant neoplasm of right ureter is C66.1 (sometimes written as C661). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is C66.1 (Malignant neoplasm of ureter) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report malignant neoplasm of right ureter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does C66.1 group to?
When malignant neoplasm of right ureter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 656, 687, 658, 657, 686, 688, with relative weights from 0.7332 to 3.2782 depending on complications. Higher weights mean higher Medicare reimbursement.
Is C66.1 a CC or MCC?
CMS lists C66.1 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 23 closely related codes in its exclusion list.
Can C66.1 be reported with C67.6?
Not as a rule. The Excludes1 note at C66, which applies to C66.1, lists "malignant neoplasm of ureteric orifice of bladder (C67.6)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What HCC is C66.1?
C66.1 (malignant neoplasm of right ureter) maps to CMS-HCC Category 22 (Bladder, Colorectal, and Other Cancers), commonly written as HCC 22, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 11 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 22.
Does C66.1 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C66.1 adds a risk adjustment factor of about 0.363 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.314 to 0.410 depending on the payment segment). A more severe related category (HCC 17, HCC 18, HCC 19, HCC 20, and HCC 21) supersedes it when both are reported. See the full factor table on the HCC 22 category page.
