Abstract:

Variants of Kaposi Sarcoma (KS) can mimic benign lesions such as pyogenic granuloma, (PG). HHV-8 expression is often used to differentiate between PG and the PG-like variant of KS. We present a case wherein reliance on the IHC alone could lead to misdiagnosis. Our patient is a 78-year-old man with metastatic Kaposi’s sarcoma on the lower extremities for over four years. A biopsy of a lesion on the left foot revealed an area of KS, as well as an associated superficial nodule with a proliferation of capillaries, and a vaguely lobular pattern of growth, mimicking a pyogenic granuloma (PG). The findings caused concern for the PG-like variant of KS. But, importantly, an HHV-8 stain did not highlight the vessels in the PG-like area, despite strong and diffuse expression in the KS. Although the patient did not have local recurrence at excised sites, prior biopsies of KS lesions also indicated strong lesional expression of HHV-8, with an even distribution of endothelial cells that did not significantly express HHV-8, particularly in the dilated vessels at the base of the tissue. The lack of HHV-8 expression in the superficial nodule can be attributed to partial regression of the Kaposi’s sarcoma, rather than a PG or PG-like KS. We conjecture that the increase in small vessels may be a direct result of the regression, as can occur in regression of other lesions. We review the features of this HHV-8 negative area of a Kaposi’s sarcoma, and detail histologic clues that can help avoid misdiagnosis.

Financial Disclosure:
No current or relevant financial relationships exist.

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Richard Barth