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C48.0 ICD-10-CM Code: Malignant neoplasm of retroperitoneum

C48.0 maps to CMS-HCC V28 20. 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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Code lookupC48.0

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

C48.0

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

Malignant neoplasm of retroperitoneum

Cancer that starts in the retroperitoneum, which is the space behind the abdominal lining. This malignant tumor develops in the tissue layer at the back of the abdomen.

Buddy the Bee presenting code insight

Buddy Insight

Malignant neoplasm of the retroperitoneum represents a severe cancer classification encompassing retroperitoneal sarcomas, which are among the most challenging abdominal malignancies to manage.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 20

Coefficient HCC 20: 1.136 (Community Non-Dual Aged (CNA))

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 peritoneumC48.0Malignant neoplasm of retroperitoneum

Inclusion Terms

Official

No inclusion terms are included in this display for C48.0. Check the code and parent instructions in the Code Book.

Excludes 2

Official

No Excludes 2 notes are included in this display for C48.0. Check the code and parent instructions in the Code Book.

Related Codes

Official
C48.1Malignant neoplasm of specified parts of peritoneumC48.2Malignant neoplasm of peritoneum, unspecifiedC48.8Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum

Includes

Official

No Includes notes are included in this display for C48.0. Check the code and parent instructions in the Code Book.

Excludes 1

Official
  • Kaposi's sarcoma of connective tissue (C46.1)Inherited from C48
  • mesothelioma (C45.-)Inherited from C48

Code First

Official

No Code First sequencing instructions are included in this display for C48.0. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C48.0. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C48.0. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Pathology confirming malignant neoplasm with retroperitoneal origin
Histological subtype (liposarcoma, leiomyosarcoma, undifferentiated pleomorphic sarcoma, etc.)
Tumor size and imaging (CT/MRI) documenting extent and organ involvement
Surgical resection status and margin assessment

MEAT Support

HCC Buddy guidance
Pathology confirming malignant neoplasm with retroperitoneal origin
Histological subtype (liposarcoma, leiomyosarcoma, undifferentiated pleomorphic sarcoma, etc.)
Tumor size and imaging (CT/MRI) documenting extent and organ involvement
Surgical resection status and margin assessment

Audit Caution

HCC Buddy guidance
Confusing primary retroperitoneal tumors with retroperitoneal metastases from other cancers (kidney, colon, etc.)
Using abdominal soft tissue codes (C49.4) instead of retroperitoneal codes (C48.0) when the tumor is retroperitoneal
Not specifying the histological subtype which affects treatment planning and prognosis
Coding a retroperitoneal lymphoma under C48.0 — lymphomas have their own specific codes (C81-C86)

Common Mistakes

HCC Buddy guidance
C48.1 (Malignant neoplasm of specified parts of peritoneum) — peritoneal, not retroperitoneal location
C47.4 (Malignant neoplasm of peripheral nerves of abdomen) — nerve-origin abdominal tumor
C49.4 (Malignant neoplasm of connective/soft tissue of abdomen) — abdominal wall soft tissue, not retroperitoneum
C78.6 (Secondary malignant neoplasm of retroperitoneum) — metastatic disease, not primary retroperitoneal cancer

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 C48.0 an HCC code?

Yes. C48.0 (Malignant neoplasm of retroperitoneum) 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: C48.0 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
C48.0
Description
Malignant neoplasm of retroperitoneum
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 C48.0 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C48.0

For C48.0, 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

C48.0 is the ICD-10-CM diagnosis code for malignant neoplasm of retroperitoneum. Cancer that starts in the retroperitoneum, which is the space behind the abdominal lining. This malignant tumor develops in the tissue layer at the back of the abdomen. C48.0 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, C48.0 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 C48.0; 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.

Retroperitoneum is distinct from peritoneum; do not confuse with C48.1. For C48.0, 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 C48.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Retroperitoneum is distinct from peritoneum; do not confuse with C48.1
  • •Common sites include retroperitoneal sarcomas; document histology and specific location when available

Clinical Significance

Malignant neoplasm of the retroperitoneum represents a severe cancer classification encompassing retroperitoneal sarcomas, which are among the most challenging abdominal malignancies to manage.

Documentation Requirements

  • ✓Pathology confirming malignant neoplasm with retroperitoneal origin
  • ✓Histological subtype (liposarcoma, leiomyosarcoma, undifferentiated pleomorphic sarcoma, etc.)
  • ✓Tumor size and imaging (CT/MRI) documenting extent and organ involvement
  • ✓Surgical resection status and margin assessment
  • ✓Distinction from retroperitoneal metastasis (secondary malignancy would use C78 codes)

Commonly Confused Codes

  • •C48.1 (Malignant neoplasm of specified parts of peritoneum): peritoneal, not retroperitoneal location
  • •C47.4 (Malignant neoplasm of peripheral nerves of abdomen): nerve-origin abdominal tumor
  • •C49.4 (Malignant neoplasm of connective/soft tissue of abdomen): abdominal wall soft tissue, not retroperitoneum
  • •C78.6 (Secondary malignant neoplasm of retroperitoneum): metastatic disease, not primary retroperitoneal cancer

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└C48.0Malignant neoplasm of retroperitoneum
└C48.0Malignant neoplasm of retroperitoneum

Also searched as

  • C48 0
  • C480

For C48.0, 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.

C48.0 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 C48.0. 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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Open C48.0 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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