Kaposi Sarcoma with Abscessing Clinicopathologic Morphology

Abstract

Background: The AIDS epidemic heralded an expanded spectrum of Kaposi sarcoma (KS) variants but to date KS masquerading as an abscess on clinical and histopathological assessment is undocumented. Methods: This 3 year retrospective study re-appraised the clinicopathological profile of all biopsies of KS that presented as abscesses clinically and demonstrated abscessing or suppurative microscopic features. Results: 10 males and 9 females form the study cohort. The clinical diagnosis in 11 patients was exclusively that of an abscess. Tuberculosis and abscess were clinical differential diagnoses in 8 patients. The average CD4 count was 261 cells/mm3. Abscessing KS was a sentinel of HIV infection and AIDS in 4 patients. Of 11 patients on HAART, 3 were virally suppressed. The pathology appeared within 3 months of HAART commencement in 5 patients; repeat CD4 counts and viral load assessments were not available for scrutiny. Microscopically, 17/19 initial biopsies with abscessing morphology demonstrated typical features of KS at least focally, while 2/19 had an exclusive abscess-like morphology. Spindle cell heterogeneity was present with co-existence in all biopsies of myofibroblasts and malignant spindle cells, the latter were HHV8-LANA-1 positive. Special stains and polymerase chain reaction investigation for infections were negative and were crucial in excluding an infective cause. Sequestrum was noted focally in the exudate of one biopsy but the patient's demise precluded assessment of underlying osteitis. Folliculitis was not present. Conclusion: HHV8-LANA-1 immunostaining underpins the identification of KS that masquerades as an abscess clinically and may mimic a spectrum of infections microscopically. Heightened awareness of this inflammatory response is pivotal to its diagnosis. The exact cause of the abscessing morphology was unconfirmed in the present study, but on-going investigation is critical to determine the pathogenesis of this, hitherto undescribed, clinicopathological profile of KS, that may predicate altered therapeutic approaches.