Kaposi sarcoma is a low-grade mesenchymal tumor involving blood and lymphatic vessels. There are four variants of this disease, each presenting a different clinical manifestation: classic or sporadic, African or endemic, organ transplant-related or iatrogenic, and AIDS-related or epidemic. Kaposi sarcoma is the most common tumor among patients with HIV infection. The pulmonary involvement in Kaposi sarcoma occurs commonly in critically immunosupressed patients who commonly have had preceding mucocutaneous or digestive involvement.
The etiology of Kaposi sarcoma is not precisely established; genetic, hormonal, and immune factors, as well as infectious agents, have all been implicated. There is evidence from epidemiologic, serologic, and molecular studies that Kaposi sarcoma is associated with human herpes virus type 8 infection. The disease starts as a reactive polyclonal angioproliferative response towards this virus, in which polyclonal cells change to form oligoclonal cell populations that expand and undergo malignant transformation.
The diagnosis of pulmonary involvement in Kaposi sarcoma usually can be made by a combination of clinical, radiographic, and laboratory findings, together with the results of bronchoscopy and transbronchial biopsy. Chest high-resolution computed tomography scans commonly reveal peribronchovascular and interlobular septal thickening, bilateral and symmetric ill-defined nodules in a peribronchovascular distribution, fissural nodularity, mediastinal adenopathies, and pleural effusions. Correlation between the high-resolution computed tomography findings and the pathology revealed by histopathological analysis demonstrate that the areas of central peribronchovascular infiltration represent tumor growth involving the bronchovascular bundles, with nodules corresponding to proliferations of neoplastic cells into the pulmonary parenchyma. The interlobular septal thickening may represent edema or tumor infiltration, and areas of ground-glass attenuation correspond to edema and the filling of air spaces with blood. These findings are a result of the propensity of Kaposi sarcoma to grow in the peribronchial and perivascular axial interstitial spaces, often as continuous sheets of tumor tissue.
There is increasing evidence that HAART and an improved immune response are associated with complete or partial regression of KS lesions, a decrease in the number of patients suffering from KS, improved survival, and protection of HIV-infected patients against the development of KS. In patients using HAART, regression of the lesions correlates with a decrease in plasma HIV load and improved immune response. Some studies showed that HAART alone can lead to stabilization and regression of KS, often eliminating the need of chemotherapy and radiation therapy, and prolonging remission among patients with a complete response. Patients with pulmonary KS using HAART showed a median survival time of 1.6 years compared with a median survival time of 4 months in the pre-HAART era.
Chemotherapy may result in rapid resolution of KS-associated symptoms and thereby improve quality of life. Cytotoxic chemotherapy is indicated for patients with extensive mucocutaneous KS, rapidly progressive cutaneous disease (more than 10 new lesions per month), symptomatic visceral disease, pulmonary disease, or extensive symptomatic lymphedema. A wide variety of chemotherapeutic agents, individually and in combination, have been evaluated for the treatment of KS. The broad range of KS response rates to single agents (21-80%) is a result of differences in the efficacy of the agents tested, variations in the patient populations treated (including level of immune function, history of prior opportunistic infections, and tumor burden), and lack of standardization of the criteria used to stage these patients or to evaluate their response to treatment. In general, the phase III clinical trials completed since 1990 define the study population and treatment outcomes more rigorously, applying the ACTG staging and response criteria.
From: Orphanet Journal of Rare Diseases 2009, 4:18 doi:10.1186/1750-1172-4-18; and HIV InSite Knowledge Base Chapter 2003. Treatment of HIV-Associated Kaposi Sarcoma.