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C55 ICD-10-CM Code: Malignant neoplasm of uterus, part unspecified

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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of female genital organs (C51-C58)

C55

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Malignant neoplasm of uterus, part unspecified

This code represents cancer of the uterus (womb) when the specific part affected is not documented or specified. The uterus is the female reproductive organ where a fetus develops during pregnancy.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of uterus, part unspecified, is the broadest uterine cancer code encompassing both cervical and corpus malignancies when the specific part cannot be determined.

CMS-HCC V28

HCC 23

RAF 0.186

CMS-HCC V24

HCC 12

RAF 0.150

ACA/HHS

HCC 12

Varies by metal level

ESRD/PACE

HCC 12

RAF 0.045

RXHCC

N/A

—

Not mapped

Code Book Path

Official
C5Malignant neoplasms of female genital organs (C51-C58)
C55Malignant neoplasm of uterus, part unspecified

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C55 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C55 in this effective period.

Related Child Codes

Official

ICD-10-CM does not list child codes under C55 for this display context.

Includes

Official

ICD-10-CM does not list Includes notes for C55 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C55 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C55 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C55 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C55 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Confirmed uterine malignancy
Documentation explaining why the specific uterine part (cervix vs. corpus) cannot be determined
Histological type if available
Staging information

MEAT Support

HCC Buddy guidance
Confirmed uterine malignancy
Documentation explaining why the specific uterine part (cervix vs. corpus) cannot be determined
Histological type if available
Staging information

Audit Caution

HCC Buddy guidance
Using this code when the cervix or corpus is identifiable from biopsy, imaging, or pathology reports
This is a coding quality indicator — high usage rates suggest systematic documentation review issues
Not distinguishing between cervical cancer and endometrial cancer, which have fundamentally different staging and treatment
Failing to query the provider when the specific uterine part is not documented in the encounter note but available in referenced reports

Common Mistakes

HCC Buddy guidance
C54.9 — Corpus uteri, unspecified; more specific — identifies the cancer is in the uterine body
C53.9 — Cervix uteri, unspecified; more specific — identifies the cancer is in the cervix
C54.1 — Endometrium; the most specific and common uterine cancer code
Z85.42 — Personal history of uterine cancer; use only when no active disease remains

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is C55 an HCC code?

Yes. C55 maps to Prostate, Breast, and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Breast, Prostate, and Other Cancers and Tumors under V24).

HCC Category Mapping

V28HCC 23, Prostate, Breast, and Other Cancers and Tumors
0.186
V24HCC 12, Breast, Prostate, and Other Cancers and Tumors
0.150
ESRDHCC 12, Breast, Prostate, and Other Cancers and Tumors
0.045

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work C55 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C55

For C55to 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 C55 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C55 is the ICD-10-CM diagnosis code for malignant neoplasm of uterus, part unspecified. This code represents cancer of the uterus (womb) when the specific part affected is not documented or specified. The uterus is the female reproductive organ where a fetus develops during pregnancy. C55 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, C55 maps to Prostate, Breast, and Other Cancers and Tumors (HCC 23) with a community, non-dual, aged base RAF weight of 0.186. Under the older CMS-HCC V24 model, C55 maps to Breast, Prostate, and Other Cancers and Tumors (HCC 12) with a community, non-dual, aged base RAF weight of 0.150. 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.

Use this code only when the medical record does not specify which part of the uterus is affected (such as the corpus, fundus, or isthmus); if the location is documented, use a more specific C54.x code instead. Because C55 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 C55 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Use this code only when the medical record does not specify which part of the uterus is affected (such as the corpus, fundus, or isthmus); if the location is documented, use a more specific C54.x code instead
  • •Verify documentation for staging information (TNM stage) and histological type, as these details are often required for cancer reporting and treatment planning

Clinical Significance

Malignant neoplasm of uterus, part unspecified, is the broadest uterine cancer code encompassing both cervical and corpus malignancies when the specific part cannot be determined. This code should be extremely rare in practice because diagnostic workup for uterine cancer virtually always identifies whether the cervix or corpus is the primary site.

Documentation Requirements

  • ✓Confirmed uterine malignancy
  • ✓Documentation explaining why the specific uterine part (cervix vs. corpus) cannot be determined
  • ✓Histological type if available
  • ✓Staging information
  • ✓Evidence of comprehensive record review
  • ✓Provider query documentation for part specification

Commonly Confused Codes

  • •C54.9: Corpus uteri, unspecified; more specific: identifies the cancer is in the uterine body
  • •C53.9: Cervix uteri, unspecified; more specific: identifies the cancer is in the cervix
  • •C54.1: Endometrium; the most specific and common uterine cancer code
  • •Z85.42: Personal history of uterine cancer; use only when no active disease remains

Code Hierarchy

└C55Malignant neoplasm of uterus, part unspecified
└C55Malignant neoplasm of uterus, part unspecified

Because C55 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

C55 maps to CMS-HCC V28 category 23, Prostate, Breast, and Other Cancers and Tumors. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works.

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