What is ICD-10 code C48.8?

C48.8 is the ICD-10-CM diagnosis code for Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum. A malignant (cancerous) tumor that involves multiple overlapping areas of both the retroperitoneum (space behind the abdominal cavity) and the peritoneum (abdominal lining). C48.8 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C48.8 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C48.8 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C48.8 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does C48.8 map to under V28?

C48.8 maps to CMS-HCC V28 20 (Lung and Other Severe Cancers). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does C48.8 pay in RAF?

C48.8 carries a community, non-dual, aged (CNA) RAF weight of 1.136 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for C48.8?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C48.8, V28 maps to Lung and Other Severe Cancers at RAF 1.136 while V24 mapped to Lung and Other Severe Cancers at RAF 1.024. Both models can still appear in legacy data and in payer-specific lookback periods.

What documentation supports C48.8?

Use this code specifically when the cancer involves both retroperitoneal and peritoneal sites; do not use for tumors limited to one area Document the extent of involvement in both anatomical regions to support medical necessity Because C48.8 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. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM C48.8: Malignant neoplasm

C48.8 maps to CMS-HCC V28 20 (RAF 1.136). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC coding software

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Code lookupC48.8Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C48.8

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

Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum

A malignant (cancerous) tumor that involves multiple overlapping areas of both the retroperitoneum (space behind the abdominal cavity) and the peritoneum (abdominal lining).

Buddy Insight

Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum indicates a tumor that involves both retroperitoneal and peritoneal spaces simultaneously.

CMS-HCC V28

Mapped

HCC 20

Lung and Other Severe Cancers

RAF 1.136

CMS-HCC V24

Mapped

HCC 9

Lung and Other Severe Cancers

RAF 1.024

ACA/HHS

Mapped

HCC 9

HHS-HCC 9

Varies by metal level

ESRD/PACE

Mapped

HCC 9

Lung and Other Severe Cancers

RAF 0.181

RXHCC

Mapped

HCC 22

Cancer, Other Specified Sites

RAF 0.124

Code Book Path

Official

C48Malignant neoplasm of retroperitoneum and peritoneum

C48.8Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C48.8 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C48.8 in this effective period.

Related Child Codes

Official

C48.0Malignant neoplasm of retroperitoneum

C48.1Malignant neoplasm of specified parts of peritoneum

C48.2Malignant neoplasm of peritoneum, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for C48.8 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 C48.8 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C48.8 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C48.8 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirming malignancy involving both retroperitoneal and peritoneal spaces

Imaging documenting the overlapping nature of the tumor across both compartments

Explanation of why a single-site code (C48.0 or C48.1) is insufficient

Surgical findings describing the extent of cross-compartment involvement

MEAT Support

HCC Buddy guidance

Pathology confirming malignancy involving both retroperitoneal and peritoneal spaces

Imaging documenting the overlapping nature of the tumor across both compartments

Explanation of why a single-site code (C48.0 or C48.1) is insufficient

Surgical findings describing the extent of cross-compartment involvement

Audit Caution

HCC Buddy guidance

Using the overlapping code when the tumor is actually confined to one compartment

Confusing 'overlapping sites' (tumor spanning both spaces) with 'unspecified' (site unknown)

Not documenting that the tumor specifically crosses the retroperitoneal-peritoneal boundary

Coding metastatic spread to both compartments as a primary overlapping tumor

Common Mistakes

HCC Buddy guidance

C48.0 (Retroperitoneum) — use when tumor is confined to the retroperitoneum

C48.1 (Specified parts of peritoneum) — use when tumor is confined to the peritoneum

C48.2 (Peritoneum, unspecified) — for unknown site within peritoneum, not overlapping compartments

C78.6 (Secondary malignant neoplasm of retroperitoneum and peritoneum) — metastatic disease, not primary

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 C48.8 an HCC code?

Yes. C48.8 (Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum) maps to Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model (and Lung and Other Severe Cancers under V24), with a community non-dual aged RAF of 1.136. It is billable for payment year 2026.

Coder answer: C48.8 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: C48.8
Description: Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum
HCC (V28): HCC 20 — Lung and Other Severe Cancers
RAF: 1.136
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers

1.136

V24HCC 9, Lung and Other Severe Cancers

1.024

ESRDHCC 9, Lung and Other Severe Cancers

0.181

RxHCCHCC 22, Cancer, Other Specified Sites

0.124

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 C48.8 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C48.8

For C48.8 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 C48.8 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C48.8 is the ICD-10-CM diagnosis code for malignant neoplasm of overlapping sites of retroperitoneum and peritoneum. A malignant (cancerous) tumor that involves multiple overlapping areas of both the retroperitoneum (space behind the abdominal cavity) and the peritoneum (abdominal lining). C48.8 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, C48.8 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 1.136. Under the older V24 model, C48.8 mapped to the same category but with a base RAF weight of 1.024, 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.

Use this code specifically when the cancer involves both retroperitoneal and peritoneal sites; do not use for tumors limited to one area. Because C48.8 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 C48.8 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use this code specifically when the cancer involves both retroperitoneal and peritoneal sites; do not use for tumors limited to one area
•Document the extent of involvement in both anatomical regions to support medical necessity

Clinical Significance

Malignant neoplasm of overlapping sites of retroperitoneum and peritoneum indicates a tumor that involves both retroperitoneal and peritoneal spaces simultaneously. This reflects extensive disease requiring complex surgical planning and typically indicates advanced-stage malignancy with significant treatment implications.

Documentation Requirements

✓Pathology confirming malignancy involving both retroperitoneal and peritoneal spaces
✓Imaging documenting the overlapping nature of the tumor across both compartments
✓Explanation of why a single-site code (C48.0 or C48.1) is insufficient
✓Surgical findings describing the extent of cross-compartment involvement
✓Treatment plan addressing the multi-compartment disease

Commonly Confused Codes

•C48.0 (Retroperitoneum): use when tumor is confined to the retroperitoneum
•C48.1 (Specified parts of peritoneum): use when tumor is confined to the peritoneum
•C48.2 (Peritoneum, unspecified): for unknown site within peritoneum, not overlapping compartments
•C78.6 (Secondary malignant neoplasm of retroperitoneum and peritoneum): metastatic disease, not primary