Kaposi sarcoma

Article Contributors:

Sean Klepper M.D.

Stephen Lyle, M.D., Ph.D.

Clinical Features:

A vascular neoplasm of intermediate malignant potential that primarily affects the skin, but which may affect multiple other organs as well.
Apparently caused by human herpes virus-8 (HHV-)
Several clinical forms exist:
- Classic (or European):
  - Most commonly affects older men of Ashkenazi Jewish or Mediterranean origin
  - Typically begins on the distal lower extremities, followed by spread and coalescence of the lesions, with lesions of different stages often present in a single patient
  - Indolent course
- African (endemic):
  - Common in equatorial Africa
  - Male predominance, typically affecting children and young adults
  - Heterogeneity of clinical presentation, ranging from nodular lesions pursuing an indolent course to florid involvement of the skin and/or lymph nodes, sometimes with bone involvement
- AIDS-associated (epidemic):
  - Among patients with AIDS, by far the most common in homosexual males
  - Typically presents as a few small pink to violaceous lesions on the upper body
  - Often progress to disseminated disease
- Immunosuppression:
  - Most common in the setting of organ transplantation
  - As is the case with the classic form of Kaposi sarcoma, there is a predisposition for individuals of Ashkenazi Jewish or Mediterranean descent, but women are more commonly affected than in the classic form.
  - May present at multiple cutaneous or visceral locations
  - Tends to progress to disseminated disease, but the lesions often regress upon reduction of immunosuppression
- Rare variants are the Stewart-Treves-like variant which occurs many years after an ipsilateral radical mastectomy in the setting of chronic lymphemema, and the lymphangioma-like variant, which often presents clinically as a bulla.

Histologic Features:

Kaposi sarcoma evolves histologically through three stages: patch, plaque and nodular.
Plaque stage:
- Inconspicuous proliferation of bland, angulated, thin-walled blood vessels which tend to surround non-neoplastic dermal blood vessels and adnexae.
- The features may be quite subtle, but a clue to the diagnosis is that the neoplastic vessels show slit-like, angulated lumina.
- An additional helpful feature when present is the promontory sign, a term used for the finding of neoplastic vessels protruding into the lumen of a pre-existing vessel or surrounding and "isolating" a normal dermal structure.
- In the early plaque stage, the vascular proliferation is confined to the reticular dermis, often only the superficial aspects of it; in later lesions, the entire dermis is involved.
- A perivascular lymphocytic infiltrate, often also containing some plasma cells, is typically present.
- Additional helpful, but not diagnostic, features that may sometimes be seen are: scattered bland spindle cells associated with the neoplastic vessels, apoptotic endothelial cells, extravasated erythrocytes, hemosiderin deposition and PAS-positive hyaline globules.
Patch stage:
- At this stage, the lesion fills the entire dermis and extends into the superficial subcutis.
- The defining feature is the presence of bland spindle cells interspersed between dermal collagen bundles.
- Present between the spindle cells are irregular, slit-like vascular channels containing scant erythrocytes.
- The perivascular lymphoplasmacytic infiltrate seen in the plaque stage remains present.
- Hemosiderin deposition and hyaline globules are more prominent than in the plaque stage.
- The periphery of the lesion shows features identical to those of the plaque stage.
Nodular stage:
- Dense proliferation of mildly to moderately atypical spindle cells in intersecting fascicles
- Interspersed among the spindle cells are slit-like vascular channels containing erythrocytes.
- Mitotic figures may be numerous.
- An associated lymphoplasmacytic infiltrate is present.
- Apoptoses, hemosiderin deposition and hyaline globules are frequent.
- Ectatic blood vessels and lymphatics are often present at the periphery of the tumor nodules.
Immunohistochemically, Kaposi sarcoma is positive for C31, CD34 and CD40, weakly positive for Ulex europaeus and negative to weakly positive for factor VIII-related antigen.