C51.1
BillableMalignant neoplasm of labium minus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C51.1 an HCC code?
Yes. C51.1 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 C51.1
For C51.1 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 C51.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C51.1 is the ICD-10-CM diagnosis code for malignant neoplasm of labium minus. Cancer that develops in the smaller inner folds of the female external genitalia (labia minora). C51.1 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, C51.1 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, C51.1 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.
Document the histological type and grade when available for treatment planning. Because C51.1 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 C51.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document the histological type and grade when available for treatment planning
- •Note any involvement of adjacent structures for proper staging classification
Clinical Significance
Malignant neoplasm of the labium minus is a vulvar cancer involving the inner, smaller folds of the female external genitalia. This location may present diagnostic challenges as tumors here can extend to involve the vaginal introitus or clitoris. Early-stage vulvar cancer of the labium minus may be treated with wide local excision, while advanced disease may require radical vulvectomy.
Documentation Requirements
- ✓Anatomical site confirmed as labium minus specifically
- ✓Histological type and grade
- ✓TNM staging with depth of stromal invasion
- ✓Inguinofemoral lymph node status
- ✓Human Papillomavirus association if documented
- ✓Surgical margins status if resection performed
- ✓Extension to adjacent structures documented
Commonly Confused Codes
- •C51.0 — Malignant neoplasm of labium majus; outer fold versus inner fold distinction
- •C51.2 — Malignant neoplasm of clitoris; adjacent but distinct anatomical structure
- •C51.8 — Overlapping sites of vulva; use when tumor involves both labia or extends across multiple structures
- •C52 — Malignant neoplasm of vagina; if tumor extends from labium minus to vaginal introitus, determine the primary site