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C48.2 ICD-10-CM Code: Malignant neoplasm of peritoneum, unspecified

C48.2 maps to CMS-HCC V28 20. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of mesothelial and soft tissue (C45-C49)

C48.2

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

Malignant neoplasm of peritoneum, unspecified

A malignant (cancerous) tumor that develops in the peritoneum, which is the thin membrane lining the abdominal cavity, when the specific location within the peritoneum is not specified.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of peritoneum, unspecified is a non-specific code that should trigger a query for more detailed anatomical information.

CMS-HCC V28

HCC 20

Code-level coefficient reference

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 009

Code-level coefficient reference

ESRD/PACE

HCC 9

Code-level coefficient reference

RXHCC

HCC 22

Code-level coefficient reference

Code Book Path

Official
C48Malignant neoplasm of retroperitoneum and peritoneum
C48.2Malignant neoplasm of peritoneum, unspecified

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C48.2 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C48.2 in this effective period.

Related Child Codes

Official
C48.0Malignant neoplasm of retroperitoneum
C48.1Malignant neoplasm of specified parts of peritoneum
C48.8Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum

Includes

Official

ICD-10-CM does not list Includes notes for C48.2 in this effective period.

Excludes 1

Official
  • Kaposi's sarcoma of connective tissue (C46.1)
  • mesothelioma (C45.-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C48.2 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C48.2 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C48.2 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Pathology confirming primary peritoneal malignancy
Documentation explaining why specific peritoneal site is unknown
Evidence of provider query attempt for site specification
Imaging showing peritoneal involvement

MEAT Support

HCC Buddy guidance
Pathology confirming primary peritoneal malignancy
Documentation explaining why specific peritoneal site is unknown
Evidence of provider query attempt for site specification
Imaging showing peritoneal involvement

Audit Caution

HCC Buddy guidance
Using the unspecified code when operative or pathology reports specify the peritoneal site
Not querying the provider to obtain more specific location information
Confusing primary peritoneal malignancy with carcinomatosis from another primary site
Using C48.2 for peritoneal mesothelioma when C45.1 is the correct code

Common Mistakes

HCC Buddy guidance
C48.1 (Specified parts of peritoneum) — preferred when any specific peritoneal site is documented
C48.0 (Retroperitoneum) — anatomically distinct from peritoneum
C78.6 (Secondary malignant neoplasm of peritoneum) — metastatic disease, not primary
C45.1 (Mesothelioma of peritoneum) — specific histological type that has its own code

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 C48.2 an HCC code?

Yes. C48.2 (Malignant neoplasm of peritoneum, unspecified) maps to HCC 20, Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 1.136. 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: C48.2 is billable and maps to V28 HCC 20, Lung and Other Severe Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C48.2
Description
Malignant neoplasm of peritoneum, unspecified
HCC (V28)
HCC 20 — Lung and Other Severe Cancers
RAF reference coefficient
1.136
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers
1.136
ESRDHCC 9, Lung and Other Severe Cancers
Not separately weighted
RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors
Not separately weighted

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 C48.2 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for C48.2

For C48.2 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 C48.2 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C48.2 is the ICD-10-CM diagnosis code for malignant neoplasm of peritoneum, unspecified. A malignant (cancerous) tumor that develops in the peritoneum, which is the thin membrane lining the abdominal cavity, when the specific location within the peritoneum is not specified. C48.2 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of mesothelial and soft tissue (c45-c49).

Under the CMS-HCC V28 risk adjustment model, C48.2 maps to Lung and Other Severe Cancers (HCC 20) with a source-labeled community, non-dual, aged reference coefficient of 1.136. No V24 mapping is shown for C48.2; use the applicable model and payment year when reviewing the V28 mapping. 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. 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.

Use this code only when the peritoneal cancer site is unspecified; if a specific location is documented, use a more specific C48 code. Because C48.2 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 C48.2 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 peritoneal cancer site is unspecified; if a specific location is documented, use a more specific C48 code
  • •This code is often used for peritoneal mesothelioma or primary peritoneal cancer when exact anatomical location is unclear

Clinical Significance

Malignant neoplasm of peritoneum, unspecified is a non-specific code that should trigger a query for more detailed anatomical information. While it carries the same high HCC weight as other C48 codes, unspecified codes carry elevated audit risk and should be used only when specific peritoneal sites cannot be determined.

Documentation Requirements

  • ✓Pathology confirming primary peritoneal malignancy
  • ✓Documentation explaining why specific peritoneal site is unknown
  • ✓Evidence of provider query attempt for site specification
  • ✓Imaging showing peritoneal involvement
  • ✓Distinction from secondary/metastatic peritoneal disease

Commonly Confused Codes

  • •C48.1 (Specified parts of peritoneum): preferred when any specific peritoneal site is documented
  • •C48.0 (Retroperitoneum): anatomically distinct from peritoneum
  • •C78.6 (Secondary malignant neoplasm of peritoneum): metastatic disease, not primary
  • •C45.1 (Mesothelioma of peritoneum): specific histological type that has its own code

Child Codes

C48.0Malignant neoplasm of retroperitoneum
HCC 20
C48.1Malignant neoplasm of specified parts of peritoneum
HCC 20
C48.2Malignant neoplasm of peritoneum, unspecified
HCC 20
C48.8Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum
HCC 20

Code Hierarchy

└C48Malignant neoplasm of retroperitoneum and peritoneum└C48.2Malignant neoplasm of peritoneum, unspecified
└C48.2Malignant neoplasm of peritoneum, unspecified

Because C48.2 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment.

C48.2 maps to CMS-HCC V28 category 20, Lung and Other Severe Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C48.2. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

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