What is ICD-10 code C46.1?

C46.1 is the ICD-10-CM diagnosis code for Kaposi's sarcoma of soft tissue. A cancer of blood vessel cells in soft tissues (muscles, fat, connective tissue) that can occur internally or superficially. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C46.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C46.1 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. C46.1 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. C46.1 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 C46.1 map to under V28?

C46.1 maps to CMS-HCC V28 HCC 21 (Lymphoma and Other Cancers). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

What documentation supports C46.1?

Soft tissue Kaposi's sarcoma may involve multiple anatomical sites; document all involved areas and whether lesions are localized or disseminated Distinguish from skin-only involvement (C46.0) by confirming involvement of deeper soft tissue structures Because C46.1 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 C46.1: Kaposi's sarcoma of soft

C46.1 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

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Code lookupC46.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C46.1

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

Kaposi's sarcoma of soft tissue

A cancer of blood vessel cells in soft tissues (muscles, fat, connective tissue) that can occur internally or superficially.

Buddy Insight

Kaposi sarcoma of soft tissue indicates deeper tissue involvement beyond the skin surface, suggesting more advanced or aggressive disease.

CMS-HCC V28

Mapped

HCC 21

Lymphoma and Other Cancers

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 010

HHS-HCC 010 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

Code-level coefficient reference

RXHCC

Mapped

HCC 20

Lung, Kidney, and Other Cance...

Code-level coefficient reference

Code Book Path

Official

C46Kaposi's sarcoma

C46.1Kaposi's sarcoma of soft tissue

Inclusion Terms

Official

Kaposi's sarcoma of blood vessel
Kaposi's sarcoma of connective tissue
Kaposi's sarcoma of fascia
Kaposi's sarcoma of ligament
Kaposi's sarcoma of lymphatic(s) NEC

Excludes 2

Official

Kaposi's sarcoma of lymph glands and nodes (C46.3)

Related Child Codes

Official

C46.0Kaposi's sarcoma of skin

C46.2Kaposi's sarcoma of palate

C46.3Kaposi's sarcoma of lymph nodes

C46.4Kaposi's sarcoma of gastrointestinal sites

C46.5Kaposi's sarcoma of lung

Includes

Official

ICD-10-CM does not list Includes notes for C46.1 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C46.1 in this effective period.

Code First

Official

any human immunodeficiency virus [HIV] disease (B20)

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C46.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C46.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirmation of Kaposi sarcoma in soft tissue structures (muscle, fat, connective tissue)

Distinction from skin-only disease — documentation must specify deeper tissue involvement

Underlying immunodeficiency status and current treatment

Imaging studies confirming soft tissue mass or infiltration

MEAT Support

HCC Buddy guidance

Pathology confirmation of Kaposi sarcoma in soft tissue structures (muscle, fat, connective tissue)

Distinction from skin-only disease — documentation must specify deeper tissue involvement

Underlying immunodeficiency status and current treatment

Imaging studies confirming soft tissue mass or infiltration

Audit Caution

HCC Buddy guidance

Defaulting to C46.0 (skin) when documentation indicates extension into subcutaneous or deeper soft tissue

Failing to differentiate between skin involvement with dermal extension versus true soft tissue involvement

Not reporting B20 (Human Immunodeficiency Virus disease) as a concurrent code when applicable

Coding historical Kaposi sarcoma as active without current documentation supporting ongoing disease

Common Mistakes

HCC Buddy guidance

C46.0 (Kaposi sarcoma of skin) — use for cutaneous-only disease; C46.1 requires deeper soft tissue involvement

C49._ (Malignant neoplasm of connective and soft tissue) — other sarcoma types (not Kaposi) of soft tissue

C46.9 (Kaposi sarcoma, unspecified) — avoid when soft tissue involvement is documented

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 C46.1 an HCC code?

Yes. C46.1 (Kaposi's sarcoma of soft tissue) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. 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: C46.1 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C46.1
Description: Kaposi's sarcoma of soft tissue
HCC (V28): HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient: 0.671
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers

0.671

ESRDHCC 10, Lymphoma and Other Cancers

Not separately weighted

RxHCCHCC 20, Lung, Kidney, and Other Cancers; Secondary Cancer of Lymph Nodes and Other Sites

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 C46.1 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for C46.1

For C46.1 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 C46.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C46.1 is the ICD-10-CM diagnosis code for kaposi's sarcoma of soft tissue. A cancer of blood vessel cells in soft tissues (muscles, fat, connective tissue) that can occur internally or superficially. C46.1 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, C46.1 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. No V24 mapping is shown for C46.1; 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.

Soft tissue Kaposi's sarcoma may involve multiple anatomical sites; document all involved areas and whether lesions are localized or disseminated. Because C46.1 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 C46.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Soft tissue Kaposi's sarcoma may involve multiple anatomical sites; document all involved areas and whether lesions are localized or disseminated
•Distinguish from skin-only involvement (C46.0) by confirming involvement of deeper soft tissue structures

Clinical Significance

Kaposi sarcoma of soft tissue indicates deeper tissue involvement beyond the skin surface, suggesting more advanced or aggressive disease. This distinction from cutaneous-only disease is clinically significant because soft tissue involvement often requires more intensive treatment and indicates a worse prognosis.

Documentation Requirements

✓Pathology confirmation of Kaposi sarcoma in soft tissue structures (muscle, fat, connective tissue)
✓Distinction from skin-only disease — documentation must specify deeper tissue involvement
✓Underlying immunodeficiency status and current treatment
✓Imaging studies confirming soft tissue mass or infiltration
✓Assessment of extent of disease (localized versus disseminated)

Excludes 2, Not included here, may code separately

Kaposi's sarcoma of lymph glands and nodes (C46.3)

Commonly Confused Codes

•C46.0 (Kaposi sarcoma of skin): use for cutaneous-only disease; C46.1 requires deeper soft tissue involvement
•C49._ (Malignant neoplasm of connective and soft tissue): other sarcoma types (not Kaposi) of soft tissue
•C46.9 (Kaposi sarcoma, unspecified): avoid when soft tissue involvement is documented