Kaposi's sarcoma: a natural model of interrelationships between viruses, immunologic responses, genetics, and oncogenesis

Kaposi's sarcoma: etiology and pathogenesis, inducing factors, causal associations, and treatments: facts and controversies

Kaposi's sarcoma (KS), an angioproliferative disorder, has a viral etiology and a multifactorial pathogenesis hinged on an immune dysfunction. The disease is multifocal, with a course ranging from indolent, with only skin manifestations to fulminant, with extensive visceral involvement. In the current view, all forms of KS have a common etiology in human herpesvirus (HHV)-8 infection, and the differences among them are due to the involvement of various cofactors. In fact, HHV-8 infection can be considered a necessary but not sufficient condition for the development of KS, because further factors (genetic, immunologic, and environmental) are required. The role of cofactors can be attributed to their ability to interact with HHV-8, to affect the immune system, or to act as vasoactive agents. In this contribution, a survey of the current state of knowledge on many and various factors involved in KS pathogenesis is carried out, in particular by highlighting the facts and controversies about the role of some drugs (quinine analogues and angiotensin-converting enzyme inhibitors) in the onset of the disease. Based on these assessments, it is possible to hypothesize that the role of cofactors in KS pathogenesis can move toward an effect either favoring or inhibiting the onset of the disease, depending on the presence of other agents modulating the pathogenesis itself, such as genetic predisposition, environmental factors, drug intake, or lymph flow disorders. It is possible that the same agents may act as either stimulating or inhibiting cofactors according to the patient’s genetic background and variable interactions.

Treatment guidelines for each form of KS are outlined, because a unique standard therapy for all of them cannot be considered due to KS heterogeneity. In most cases, therapeutic options, both local and systemic, should be tailored to the patient’s peculiar clinical conditions.

Human herpesvirus 8

Human herpesvirus 8 (HHV 8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV) is a g2 herpesvirus and the most recently identified human tumor virus. HHV 8 has been consistently implicated in the pathogenesis of all clinical variants of Kaposi's sarcoma, as well as in the plasma cell variant of multicentric Castleman's disease and primary effusion lymphomas. Pathogenicity of the virus is increased in the host who is immunosuppressed, either iatrogenically or through H1V-1 infection. The HHV 8 genome contains several homologues of cellular genes that regulate cell growth and differentiation, and the exact mechanisms of the virus' oncogenicity using molecular piracy are still being investigated and elucidated. In this article, the authors review the epidemiology, transmission, clinical manifestations, and molecular genetics of HHV 8 infection and provide a summary of the current treatment modalities available to the clinician.

Kaposi's sarcoma in the hand seen as an arteriovenous malformation

A case of Kaposi's sarcoma, which was initially thought to represent an arteriovenous malformation, is described. Angiographic findings were misleading, and careful histopathological analysis of such lesions is advocated so that correct treatment may be carried out.

Genetically determined coincidence of Kaposi sarcoma and psoriasis in an HIV-negative patient after prednisolone treatment. Spontaneous regression 8 months after discontinuing therapy

We report the case of drug-induced, acrolocalized Kaposi sarcoma (KS), arising multicentrically in both palms and soles of a male patient who has had widespread psoriasis since 12 years of age. This 59-year-old man, of Mediterranean origin, was HIV antibody-negative and had received oral prednisolone treatment over 5 months for chronic obstructive lung disease (initial dose: 75 mg/d). Eight months after discontinuing oral treatment the KS nodules regressed spontaneously and finally disappeared completely without additional treatment. Light and electron microscopic investigations confirmed the diagnosis of KS, whereas laboratory tests excluded HIV infection and suggested mild immune dysfunction. The existence of HLA loci predisposing to KS and to psoriasis (A1, DR5, DR7, DR11) was characteristic for the simultaneous occurrence of these two diseases. This case report demonstrates the complex interrelationships between genetic predisposition, drugs leading to immune suppression, and the evolution of an unusual neoplasm.

Detection of cytomegalovirus DNA in classic and epidemic Kaposi's sarcoma by in situ hybridization

Several lines of evidence have suggested an etiologic association of cytomegalovirus (CMV) with Kaposi's sarcoma. This contention is supported by a pathoepidemiologic survey of 54 cases of acquired immunodeficiency syndrome (AIDS) at our own institution. Of the 27 patients with documented Kaposi's sarcoma, 24 (89%) showed histologic evidence of CMV infection (cytomegalic cells with viral inclusions), whereas only 9 (33%) of the patients with AIDS without Kaposi's sarcoma showed hallmarks of CMV infection. In an attempt to address this question further, we have searched for the presence of CMV nucleic acid sequences in a series of 25 patients with AIDS and Kaposi's sarcoma, using the technique of in situ DNA hybridization. The reliability of the in situ technique is demonstrated, and the technique is shown to be more sensitive than the detection of viral inclusions within Kaposi's sarcoma lesions by routine light microscopy. However, only 20% of our cases showed evidence of CMV involvement, and the CMV-positive cells within the affected Kaposi's sarcoma lesions were few and sparsely distributed. In addition, a companion series of 6 elderly patients with "classic" Kaposi's sarcoma showed no evidence of CMV infection by either conventional microscopy or in situ hybridization. These results do not support the notion of a strong association between Kaposi's sarcoma and CMV, unless the CMV sequences are present at a copy number too low for detection by these methods. The implications of these findings in light of current theories of CMV oncogenesis are discussed.

The incidence of second malignancies in subsets of Kaposi's sarcoma

There is strong evidence linking Kaposi's sarcoma with an increased risk of developing a second primary malignancy. This risk of a second malignancy appears to depend in part on the clinical setting in which Kaposi's sarcoma develops. This paper examines these risks by relating them to specific subsets of Kaposi's sarcoma and to specific types of second malignancies.