Kaposi sarcoma (ORPHA:33276)
A rare vascular tumor that is characterized by human herpes virus 8 (HHV-8)-induced endothelial inflammatory neoplasm that develops with various clinically distinct settings, manifesting mostly as cutaneous lesions, or mucosal or visceral involvement.
Epidemiology
More than 100 million people worldwide are infected with HHV-8, with a heterogeneous geographic distribution (high in Africa and the Mediterranean). Only a very small proportion of those infected with HHV-8 develop KS. Incidence in Europe is reported to be about 1/300,000.
Clinical description
HHV-8 infection is asymptomatic in the vast majority of cases. In some clinical contexts, the risk of developing Kaposi sarcoma (KS) is much higher, giving rise to four subtypes: Classic KS, African endemic KS, iatrogenic immunodepression KS, and AIDS-related KS. Cases affecting otherwise healthy people with no manifest immunological deficit except ''immunosenescence'' are known as classic KS (mostly reported in the Mediterranean basin) and African endemic KS (reported in sub-Saharan Africa) which affects primarily children and middle-aged men. Iatrogenic KS is mostly found in recipients of solid organs. Lastly, AIDS-related KS affects mainly homosexual men. A fifth subtype has been recently identified affecting non HIV infected homosexual men. Skin lesions manifest as solitary, localized or disseminated patches, or macular/papular eruptions, which progress to nodular plaques or lesions on any area of the skin. Progression is highly variable with lesions at different stages possibly occurring in the same individual. Lymph node and visceral involvement may be found in some forms especially iatrogenic and AIDS-KS. The oral cavity and the gastrointestinal tract (GI) are frequently affected. Pulmonary involvement is less common but may be life-threatening. Lymphedema of the face, genitalia and lower extremities may be found especially in classic and endemic KS. Some rare patients do not present skin lesions.
Etiology
All known forms of KS are caused by HHV-8 infection. The exact routes of HHV-8 transmission are currently unknown but both sexual and non-sexual modes are suspected. The highest levels of HHV-8 shedding are found in saliva.
Diagnostic methods
KS is usually diagnosed on the basis of disseminated skin lesions, sometimes with lymph node and visceral involvement. Skin biopsy reveals neoangiogenesis and proliferating spindle-shaped cells, admixed with a variable chronic inflammatory infiltrate. Immunohistochemistry using monoclonal antibody against latent protein of HHV-8 is useful to differentiate KS from other angioproliferative tumors. Imaging techniques may be required to identify systemic disease but there is no consensus on systematic explorations.
Differential diagnosis
The differential diagnosis may include bacillary angiomatosis, hemosiderotic hemangioma, fibrous histiocytoma, interstitial granuloma annulare, arteriovenous malformations, and pyogenic granuloma.
Management and treatment
No specific treatment recommendations have been established. Treatment depends on the KS type and presence of localized or systemic involvement. The main aim of treatment is to restore immunity. Rapamycin or everolimus can be used in organ transplant recipients, and discontinuation or reduction of immunosuppressive therapy is recommended. Antiretroviral therapy should be systematically prescribed in KS-AIDS to prevent or reduce lesions. For localized lesions, radiotherapy, topical gels (alitretinoin), intralesional injections (vinblastine or bleomycin), surgery, or cryotherapy can be used. Visceral involvement generally requires systemic therapy with antiproliferative agents (taxanes and liposomal anthracyclins or interferon alpha 2b). Use of steroids should be avoided in patients with KS.
Prognosis
KS ranges from an indolent disorder to an aggressive disease with significant morbidity and mortality. It is generally not life-threatening in most forms, but may have major psychosocial implications and significant impact on quality of life.

                            Last update: 
                            May 2019


                            - Expert reviewer(s): 
                            Pr Nicolas DUPIN