Sean Klepper M.D.
Stephen Lyle, M.D., ...
- 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
- 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.
- 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.