C57.21 ICD-10-CM Code: Malignant neoplasm of right round ligament
C57.21 maps to CMS-HCC V28 22. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools
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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of female genital organs (C51-C58)
C57.21
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMalignant neoplasm of right round ligament
Cancer that develops in the right round ligament, a cord-like structure that helps support the uterus on the right side.
Buddy Insight
Right round ligament malignancy is an exceedingly rare tumor that may present as a right inguinal mass mimicking a hernia or lymphadenopathy.
CMS-HCC V28
MappedHCC 22
Coefficient HCC 22: 0.363 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 011
Code-level coefficient reference
ESRD/PACE
MappedHCC 10
Code-level coefficient reference
RXHCC
MappedHCC 22
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for C57.21. Check the code and parent instructions in the Code Book.
Excludes 2
OfficialNo Excludes 2 notes are included in this display for C57.21. Check the code and parent instructions in the Code Book.
Related Codes
Includes
Official- malignant neoplasm of skin of female genital organsInherited from C51-C58
Excludes 1
OfficialNo Excludes 1 notes are included in this display for C57.21. Check the code and parent instructions in the Code Book.
Code First
OfficialNo Code First sequencing instructions are included in this display for C57.21. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for C57.21. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for C57.21. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is C57.21 an HCC code?
Yes. C57.21 (Malignant neoplasm of right round ligament) maps to HCC 22, Bladder, Colorectal, and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.363. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: C57.21 is billable and maps to V28 HCC 22, Bladder, Colorectal, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- C57.21
- Description
- Malignant neoplasm of right round ligament
- HCC (V28)
- HCC 22 — Bladder, Colorectal, and Other Cancers
- RAF reference coefficient
- 0.363
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work C57.21 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C57.21
For C57.21, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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What This Code Means
C57.21 is the ICD-10-CM diagnosis code for malignant neoplasm of right round ligament. Cancer that develops in the right round ligament, a cord-like structure that helps support the uterus on the right side. C57.21 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of female genital organs (c51-c58).
Under the CMS-HCC V28 risk adjustment model, C57.21 maps to Bladder, Colorectal, and Other Cancers (HCC 22) with a source-labeled community, non-dual, aged reference coefficient of 0.363. No V24 mapping is shown for C57.21; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Ensure right side is explicitly documented before coding; round ligament cancers are uncommon. For C57.21, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, and MEAT documentation criteria for C57.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure right side is explicitly documented before coding; round ligament cancers are uncommon
- •Verify this is not a metastatic cancer from another primary site
Clinical Significance
Right round ligament malignancy is an exceedingly rare tumor that may present as a right inguinal mass mimicking a hernia or lymphadenopathy. Correct anatomical identification and laterality documentation are critical for accurate coding and to ensure appropriate surgical management and surveillance.
Documentation Requirements
- ✓Documentation specifying right-sided round ligament involvement
- ✓Pathologic confirmation of malignancy
- ✓Histologic type and grade
- ✓Staging and treatment plan
- ✓Confirmation that this is a primary neoplasm rather than metastatic disease