Ectopic hamartomatous thymoma: a case report showing CD99+ lymphocytes and a low proliferation index.

Lee, Shi Nae; Cho, Min Sun; Koo, Heasoo; Han, Woon Sup · Arch Pathol Lab Med · 2003

case_report · Level V

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Abstract

Ectopic hamartomatous thymoma is a rare benign tumor that consists of spindle, epithelial, and adipose cell elements. We present a case of this lesion arising in the supraclavicular region of a 59-year-old man, including the characteristic immunohistochemical and ultrastructural findings. DNA flow cytometry revealed diploidy with a low proliferation index (6.73%). The tumor contained CD99+ lymphocytes; CD99 (MIC2) can serve as a useful marker of immature T cells. These findings suggest that ectopic hamartomatous thymoma may develop from the third branchial pouch or thymic anlage.

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