ICD-10 Code C54.2: Malignant neoplasm of myometrium

Key Takeaways

ICD-10 Code C54.2 is the billable, site-specific diagnosis code for malignant neoplasm of the myometrium (the muscular wall of the uterus), valid for FY 2026 reimbursement.

C54.2 is distinct from C54.1 (endometrium): pathology confirmation of myometrial involvement is required before assigning C54.2 rather than the unspecified C54.9.

Research published in Pharmacoepidemiology and Drug Safety explicitly excludes C54.2 from endometrial cancer case-finding algorithms, making site-specific documentation critical for claims accuracy.

Pabau’s claims management software and AI-powered clinical documentation tools help gynecologic oncology practices capture the site-specific detail needed to support C54.2 without querying or audit risk.

ICD-10 Code C54.2 is the billable diagnosis code for malignant neoplasm of the myometrium, the smooth-muscle wall of the uterus. It is most commonly assigned for uterine leiomyosarcoma confirmed by surgical pathology, and it applies only when documentation specifies myometrial involvement rather than the endometrium or an unspecified corpus uteri site.

This reference covers the classification hierarchy, billable status, key distinctions from adjacent C54 codes, documentation requirements, MS-DRG groupings, and the ICD-9 crosswalk for C54.2.

ICD-10 Code C54.2: Definition and clinical description

ICD-10 Code C54.2 designates a primary malignant neoplasm arising from the myometrium, the thick smooth-muscle layer that forms the middle wall of the uterus between the endometrium (inner lining) and the serosa (outer peritoneal covering). Tumors assigned to this code originate in or primarily involve the myometrial tissue itself rather than the endometrial glands and stroma that are the source of the far more common endometrial carcinomas.

The most clinically significant malignancy coded under C54.2 is uterine leiomyosarcoma, a rare and aggressive smooth-muscle tumor that accounts for roughly 1-2% of all uterine malignancies. Other histologic subtypes coded here when they arise from myometrial stroma include undifferentiated uterine sarcoma with myometrial origin and, in some pathological interpretations, endometrial stromal sarcoma when confirmed to primarily involve the muscle layer rather than the endometrial surface. The pathology report is the authoritative document for code selection in every case.

Clinicians at OB/GYN practices and gynecologic oncology programs need this code readily available alongside C54.1 and C54.9. The clinical picture of myometrial malignancy often overlaps with benign leiomyomata (fibroids) on initial imaging, making pathological distinction and precise documentation especially important for coding accuracy.

Synonyms and applicable diagnoses

Multiple clinical terms map to ICD-10 Code C54.2 in the tabular index. Coders and clinicians should recognize these synonyms when reviewing operative reports and pathology narratives:

• Primary malignant neoplasm of myometrium
• Leiomyosarcoma of the uterus (when myometrial origin is confirmed)
• Malignant mesenchymal tumor of uterine muscle wall
• Uterine smooth-muscle malignancy (myometrial type)
• Sarcoma of myometrium

Note that not every uterine sarcoma maps automatically to C54.2. Carcinosarcoma of the uterus (malignant mixed Müllerian tumor) has no dedicated code and is assigned to the corpus uteri site identified in the pathology report–most often C54.1, since the majority arise from the endometrium–rather than automatically to C54.2. Always confirm the histologic type and anatomic layer against the tabular list before assigning C54.2.

Code details and classification hierarchy

Understanding where C54.2 sits in the ICD-10-CM hierarchy helps coders navigate adjacent codes and avoid misclassification. The WHO ICD-10 classification places this code within the following structure:

C54.2 is a valid, billable ICD-10-CM code for FY 2026. It carries a full code designation, meaning it can stand alone as the principal or secondary diagnosis on a claim without requiring an additional specificity digit. Verify current billable status annually against the CDC/NCHS ICD-10-CM web tool, which reflects each fiscal year’s official tabular updates.

Full C54 code family at a glance

The C54 category covers all malignant neoplasms of the corpus uteri. Each subcategory represents a distinct anatomic site within the uterine body:

• C54.0 – Malignant neoplasm of isthmus uteri (the narrow junction between the body and cervix)
• C54.1 – Malignant neoplasm of endometrium (inner mucosal lining; most common uterine cancer site)
• C54.2 – Malignant neoplasm of myometrium (middle smooth-muscle wall; leiomyosarcoma territory)
• C54.3 – Malignant neoplasm of fundus uteri
• C54.8 – Malignant neoplasm of overlapping sites of corpus uteri
• C54.9 – Malignant neoplasm of corpus uteri, unspecified (use only when documentation does not identify a specific site)

When pathology reports reference involvement of multiple uterine body sites, consider C54.8 (overlapping sites) rather than defaulting to C54.9. C54.9 should be a last resort when site specificity cannot be determined after querying the provider.

C54.2 vs. C54.1: Coding the right uterine site

The distinction between C54.2 (myometrium) and C54.1 (endometrium) is the most consequential code selection decision in the C54 family. Getting it wrong affects MS-DRG grouping, cancer registry accuracy, and population-level epidemiological research.

A 2023 peer-reviewed study in Pharmacoepidemiology and Drug Safety validated ICD-10 case-finding algorithms for endometrial cancer in US insurance claims data and explicitly excluded C54.2 from its endometrial cancer definition. That exclusion reflects a clinical reality: myometrial malignancies are biologically and prognostically distinct from endometrial carcinomas.

A common coding trap occurs when an operative note describes a “uterine mass” removed during myomectomy and the pathology returns “leiomyosarcoma.” Without a coder querying the provider to confirm myometrial origin (rather than a degenerated fibroid extending to the serosa), C54.9 or even an incorrect C54.1 may be assigned. The same site-specific coding discipline used for other organ-layer malignancies applies equally here: when in doubt, query before coding.

When to use C54.9 instead

C54.9 is appropriate only when the pathology report or clinical documentation confirms a corpus uteri malignancy but does not specify the sub-site. Per the ICD-10-CM Official Guidelines for Coding and Reporting maintained by CMS and NCHS, coders should not assume a site-specific code from ambiguous documentation. Assign C54.9 when the record genuinely cannot support C54.0, C54.1, C54.2, C54.3, or C54.8, and document the query in the medical record workflow.

Billable status, FIGO staging, and MS-DRG groupings

C54.2 is a fully billable ICD-10-CM diagnosis code, meaning it can be submitted on a claim as the sole diagnosis code for the relevant encounter without requiring an additional specificity extension. This is significant in gynecologic oncology billing, where some practitioners incorrectly treat C54.2 as a “non-specific” placeholder because myometrial malignancies are relatively rare.

FIGO staging and code interaction

The International Federation of Gynecology and Obstetrics (FIGO) staging system applies to uterine sarcomas including leiomyosarcoma. FIGO stage does not change the ICD-10-CM code assigned (C54.2 is used regardless of stage), but stage documentation directly influences the CPT procedure codes billed alongside C54.2 and the MS-DRG the case falls into.

A FIGO Stage I leiomyosarcoma confined to the uterus will group differently than a Stage IV case with distant metastasis. Coders should capture metastatic spread with additional secondary neoplasm codes (C78-C79 range) when documented.

MS-DRG groupings for C54.2

When C54.2 serves as the principal diagnosis, CMS groups the case within several MS-DRGs depending on whether a procedure was performed and the patient’s complication/comorbidity (CC/MCC) status. C54.2 maps to MS-DRG v43.0 groupings in the uterine and adnexa procedure categories. The exact DRG assignment shifts based on:

• Whether a hysterectomy or other major pelvic procedure is the principal procedure (shifts to surgical DRGs)
• Whether the encounter is medical-only (maps to medical DRGs for malignancy workup or chemotherapy administration)
• Presence of MCCs (major complications or comorbidities) vs. CCs vs. neither

Verify the current-year DRG assignment using the CDC/NCHS ICD-10-CM tool or your facility’s grouper software, as MS-DRG version numbers update annually and weightings change.

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Documentation requirements for accurate C54.2 coding

Coding C54.2 correctly depends on a clear documentation chain from the clinical encounter to the pathology report to the coding workflow. Gynecologic oncology practices that build structured documentation habits into their EHR templates can eliminate most querying delays and claim denials before they occur.

Required documentation elements

The following elements must appear in the medical record to support C54.2 on the claim:

• Pathology confirmation: A final surgical pathology report explicitly identifying the malignant tumor’s anatomic layer of origin as the myometrium
• Histologic type: Pathologist’s classification of the tumor type (e.g., leiomyosarcoma, undifferentiated uterine sarcoma with myometrial primary)
• Operative or clinical note: Surgeon’s description of the gross specimen and pre-operative assessment confirming corpus uteri involvement at the myometrial layer
• Staging documentation: FIGO stage or clinical stage narrative to support associated secondary code assignments
• Provider attestation: If pathology is ambiguous regarding the specific uterine layer involved, a provider query response confirming myometrial primary is documented before the code is assigned

Practices using structured clinical record templates for oncology consultations can embed these documentation checkpoints directly into the note-writing workflow. Capturing the pathologic layer at the time of result review, rather than during retrospective coding, dramatically reduces query volume.

EHR documentation tips for site-specific coding

Three EHR habits support consistent C54.2 documentation in gynecologic oncology:

1. Template-driven pathology review: Build a structured field in your pathology result review template that requires the clinician to select the confirmed uterine layer (endometrium / myometrium / overlapping / unspecified) before the note is signed.
2. Automated result-to-note linking: Use AI-powered clinical documentation tools that can flag a uterine malignancy result and prompt the provider to confirm anatomic specificity in real time, rather than flagging it to a coder weeks later.
3. Pre-authorization documentation: When submitting prior authorization requests for chemotherapy or radiation following a C54.2 diagnosis, include the pathology summary confirming myometrial origin. Payers reviewing authorizations for uterine cancer often request this distinction because it affects treatment protocol approval.

For practices managing claims across multiple oncology encounters, building a problem-list entry for C54.2 that carries forward across visits (with status updates for remission or recurrence) keeps the diagnosis code consistent throughout the treatment course and reduces the risk of conflicting codes across claims dates.

Sequencing rules, ICD-9 crosswalk, and related codes

Correct sequencing and awareness of adjacent codes prevent over-coding and under-coding in uterine malignancy encounters. This section covers the sequencing logic for C54.2 in common clinical scenarios, the historical ICD-9-CM equivalent, and the codes most often reported alongside C54.2.

Sequencing: principal vs. secondary diagnosis

C54.2 follows standard ICD-10-CM sequencing rules for malignant neoplasms:

• C54.2 as principal diagnosis: Used when the encounter is for the primary cancer itself, including initial staging workup, surgical resection, or radiation planning visits where the myometrial malignancy is the chief reason for the encounter.
• C54.2 as secondary diagnosis: Used when the encounter is for treatment of a complication (e.g., anemia due to the malignancy) or when a second primary cancer is also present. The condition being treated becomes the principal diagnosis; C54.2 is sequenced as an additional code.
• Chemotherapy encounter sequencing: When the encounter is specifically for administration of antineoplastic chemotherapy, Z51.11 (Encounter for antineoplastic chemotherapy) sequences first; C54.2 follows as the secondary diagnosis identifying the malignancy being treated. This sequencing rule applies across many oncology diagnosis codes and is frequently misapplied in ambulatory oncology settings.

ICD-9-CM crosswalk

The approximate ICD-9-CM equivalent of C54.2 is 182.0 (Malignant neoplasm of corpus uteri, except isthmus). This crosswalk is approximate rather than exact because ICD-9-CM code 182.0 encompasses both endometrial and myometrial malignancies of the corpus uteri without sub-site specificity. The move to ICD-10-CM in October 2015 introduced the granularity that separates C54.1 (endometrium) from C54.2 (myometrium) from C54.9 (unspecified).

When reviewing historical claims data or conducting retrospective research that spans the ICD-9/ICD-10 transition period, treat 182.0 as a parent code that may correspond to C54.0, C54.1, C54.2, or C54.9 depending on the clinical context. For bidirectional code mapping tools, the CMS ICD-10 general equivalence mapping (GEM) files provide the official forward-backward crosswalk.

Codes commonly reported with C54.2

In clinical practice, C54.2 rarely appears in isolation. The following codes are frequently reported alongside it, depending on the encounter type and disease stage:

• C55 (Malignant neoplasm of uterus, part unspecified) – Use C55 rather than C54.2 only when even corpus vs. cervix distinction cannot be made from documentation
• C78.6 (Secondary malignant neoplasm of retroperitoneum and peritoneum) – For documented peritoneal spread in advanced leiomyosarcoma
• C79.81 (Secondary malignant neoplasm of breast) – Rare metastatic pattern for high-grade uterine sarcomas
• Z85.42 (Personal history of malignant neoplasm of other parts of uterus) – For follow-up visits after curative-intent treatment of C54.2
• D25.x (Leiomyoma of uterus) – Assigned in the pre-operative setting when the mass is suspected but malignancy not yet confirmed; replace this code with C54.2 once pathology returns a malignant result
• Z51.11 (Encounter for antineoplastic chemotherapy) – Sequences first when the encounter purpose is chemotherapy administration

Practices running HIPAA-compliant billing workflows for oncology services should build problem-list templates that capture the full code set for each uterine malignancy patient, including the primary C54.2, any secondary neoplasm codes, and the current encounter-type codes (Z51.xx, Z79.xx for long-term medication use).

This prevents the common scenario where a coder on an encounter for follow-up imaging submits C54.2 as the sole code without the Z08 follow-up code (encounter for follow-up examination after completed treatment for malignant neoplasm) or the Z85.42 personal-history code that correctly describes the encounter purpose.

Conclusion

ICD-10 Code C54.2 is a site-specific, billable diagnosis code for myometrial malignancies that demands pathology-confirmed documentation before it can be assigned. The distinction between “uterine cancer” and “myometrial malignancy” looks small on paper but has real consequences for MS-DRG grouping, cancer registry accuracy, and claims audit risk. Practices that capture the anatomic layer at the point of pathology review settle that distinction before it becomes a billing problem.

Pabau’s claims management software and compliance management tools help gynecologic oncology practices build the documentation checkpoints that support site-specific coding like C54.2 throughout the treatment course. To see how Pabau handles this for oncology and women’s health practices, book a demo.

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