Soft tissue


Intermediate (locally aggressive / rarely metastasizing)

Kaposi sarcoma

Editor-in-Chief: Debra L. Zynger, M.D.
Michella Whisman, M.D.
Jerad M. Gardner, M.D.

Last author update: 22 January 2019
Last staff update: 6 October 2022 (update in progress)

Copyright: 2002-2023,, Inc.

PubMed Search: Kaposi sarcoma [title] soft tissue

Michella Whisman, M.D.
Jerad M. Gardner, M.D.
Page views in 2022: 36,863
Page views in 2023 to date: 19,628
Cite this page: Whisman M, Gardner JM. Kaposi sarcoma. website. Accessed June 8th, 2023.
Definition / general
  • Vascular neoplasm caused by human herpesvirus 8 (HHV8)
  • Tends to be indolent but may be locally aggressive
Essential features
  • Etiologic agent of all forms and cases is human herpesvirus 8 (HHV8), HHV8 immunostain will distinguish it from other vascular tumors on the differential
  • Microscopic morphology is similar for all clinical variants
  • Slit-like vascular spaces formed by spindled endothelial cells with minimal to moderate atypia; hemorrhage, hemosiderin and plasma cells are key histologic clues
  • Can histologically mimic angiosarcoma; distinction is critical, as behavior and treatment are very different
ICD coding
  • ICD-10: C46 - Kaposi sarcoma
  • Depends on the clinical variant of Kaposi sarcoma (4 subtypes) (Dermatol Ther (Heidelb) 2016;6:465):
    • Classic / sporadic
      • Elderly men > women
      • Lower extremity skin lesions
      • Central equatorial Africa, Mediterranean and Eastern European
      • May be associated with secondary malignancy
      • Clinically indolent course
    • Endemic / African
      • Lower extremity skin lesions
      • Children and young to middle aged adults
      • Not related to HIV
      • Sub-Saharan Africa
      • May be aggressive if lymph nodes involved
    • Iatrogenic
      • Predominantly transplant associated
      • Skin, visceral and mucosa involvement
    • AIDS associated
      • Patients infected with HIV1
      • Predilection for certain risk groups
        • Risk for homosexual men greater than hemophiliac
      • Affinity for skin but may be disseminated
      • Most aggressive of all Kaposi subtypes
  • Skin is predominant site
  • May also affect lymph nodes, visceral organs or mucosa
  • HHV8
Clinical features
  • Progressive, enlarging red to violaceous skin lesions (Arch Pathol Lab Med 2013;137:289)
    • Patch stage
      • Red or purple macules or patches
    • Plaque stage
      • Thickened red, purple or brown plaques
    • Tumor stage
      • Nodule formation
  • All four clinical subtypes of Kaposi may show these stages
  • Multiple different stages may be present simultaneously
  • HHV8 positive peripheral blood, as well as lesional tissue
Radiology description
Radiology images

Images hosted on other servers:

Pulmonary Kaposi sarcoma

Prognostic factors
  • Clinical variant
  • Stage of disease
  • Status of immune system
Case reports
  • No definitive cure but variety of possible treatments for palliation (Am J Clin Dermatol 2017;18:529)
  • Removal of immunosuppressive agents in iatrogenic variant
  • Highly active antiretroviral therapy (HAART) for AIDS associated variant
  • Other options include: surgical excision (of symptomatic lesions only; wide local excision usually not indicated), radiation, systemic chemotherapy, topical drugs, cryoablation therapy
Clinical images

Contributed by Mark R. Wick, M.D.

Advanced disease

Images hosted on other servers:

Reddish purple nodules


Intraoral lesion

Violaceous plaques

Gross description
  • Red to purple lesions
  • Hemorrhagic on cut surface, especially visceral lesions
Gross images

Images hosted on other servers:

Infiltration of lung parenchyma

Reddish nodules on gastric mucosa

Irregular masses in the liver

Microscopic (histologic) description
  • Patch stage:
    • Dilated vascular channels dissecting through dermal collagen
      • Promontory sign: tumor vascular channels surround and entrap native vessels (classic but uncommon feature)
    • May be very subtle in early lesions
  • Plaque stage:
    • More extensive, compressed, slit-like vascular channels infiltrating deeper dermis
    • Infiltrative proliferation of spindled endothelial cells (may resemble fibroblasts)
      • Spindle cells infiltrating and destroying eccrine coils is very characteristic
  • Tumor (nodular) stage:
    • Discrete nodules composed of intersecting fascicles of uniform spindle cells
    • Intervening blood filled spaces between spindle cells
      • Slit-like spaces (longitudinal section)
      • Sieve-like spaces (cross section)
    • Intracytoplasmic hyaline globules may be seen
  • All stages:
    • Mitoses common but pleomorphism usually minimal
      • Rare poorly differentiated cases have severe pleomorphism (must confirm with HHV8 immunostain to exclude angiosarcoma)
    • Extravasated erythrocytes and hemosiderin common findings
    • Plasma cells present in most cases

Microscopic (histologic) images

Contributed by Michella Whisman, M.D.

Early lesion subtle at low power

Dilated channels visible at higher power

Inflammatory appearance

Lymphoplasmacytic infiltrate

Hemosiderin deposition

Spindle cell proliferation

Tumor (nodular) stage

Sieve-like pattern

Blood filled channels

Spindle cells without blood

Ill defined fasicles



HHV8 can be missed at low power

HHV8 with focal positivity

Contributed by Mark R. Wick, M.D.

Hyaline globules

Cytology description
Cytology images

Contributed by Michella Whisman, M.D.

Lymph node touch prep

Positive stains
Differential diagnosis
  • Angiosarcoma
    • Infiltrative vascular channels, usually with marked nuclear atypia
    • HHV8 negative
    • Usually arises in head / neck of sun damaged elderly or at site of irradiation
  • Severe vascular stasis (acroangiodermatitis)
    • Fibroblastic spindle cell component rather than endothelial
    • Negative for vascular markers
    • HHV8 negative
  • Hobnail hemangioma (targetoid hemosiderotic hemangioma)
    • Slit-like vascular channels but no spindle cell proliferation
    • HHV8 negative
  • Spindle cell hemangioma
    • Spindled endothelial cells with slit-like channels but also has epithelioid cells
    • Biphasic: solid spindled / epithelioid zone and zone of dilated cavernous vessels
    • Usually lacks plasma cells and hemorrhage
    • HHV8 negative
  • Kaposiform hemangioendothelioma
    • Unique whorled and nodular pattern of spindled endothelial cells
    • Hemorrhage and plasma cells uncommon
    • Usually in young children or infants
    • HHV8 negative
Board review style question #1
The pictured tumor is from the foot of a 75 year old man of Mediterranean descent. The virus associated with the diagnosis also causes which of the following?

  1. Adult T cell leukemia
  2. Burkitt lymphoma
  3. Primary effusion lymphoma
  4. Squamous cell carcinoma of the cervix
Board review style answer #1
C. The pictured tumor is Kaposi sarcoma which is caused by HHV8. HHV8 may also lead to primary effusion lymphoma and multicentric Castleman disease. Squamous cell carcinoma of the cervix is caused by HPV. Burkitt lymphoma can be associated with EBV. Adult T cell leukemia is associated with HTLV1.

Comment here

Reference: Kaposi sarcoma
Board review style question #2
Which histologic finding would favor a diagnosis of Kaposi sarcoma over angiosarcoma?

  1. Infiltrative, anastomosing vascular channels
  2. History of radiation exposure
  3. Marked cytologic atypia
  4. Positive LANA1 stain
Board review style answer #2
D. Positive LANA1 stain

Comment here

Reference: Kaposi sarcoma
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