11/11. Merkel cell carcinoma with partial spontaneous regression: an immunohistochemical, ultrastructural, and TUNEL labeling study.We report a case of Merkel cell carcinoma that partially regressed after biopsy. A 76-year-old woman presented with an 1 month history of a rapidly enlarging nodule on her left cheek. After biopsy, the nodule reduced to almost half the size and was excised 1 month later. The excised specimen showed a dense cluster of lymphocytes and fibrosis around the tumor nests. In addition, lymphocytes showed apposition with tumor cells. An immunohistologically dense, even infiltration of CD4 and CD8 cells was found around the tumor nests, and more CD8 cells than CD4 cells were seen in the tumor nests. By electron microscopy (EM), apoptosis of tumor cells and lymphocytes was observed. Many apoptotic cells were also detected by in situ nick end-labeling (TUNEL) of dna-breaks, especially in the marginal area of tumor nests surrounded by dense lymphocytic infiltrates. It seems likely that T-cell immunity, which induces apoptosis of tumor cells, may have been involved in tumor regression.
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keywords = apoptosis
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