Spontaneous regression of Merkel cell carcinoma.

A 96-year-old woman presented with a rapidly enlarging lesion overlying the suprasternal notch. The lesion originated as a small, erythematous, scaly macule that rapidly increased in size over 8 weeks and became an ulcerated nodule measuring 5 cm in diameter and 4.5 cm in thickness. A 4-mm punch biopsy showed a poorly differentiated tumor with cells that were positive for CAM 5.2 and cytokeratin 20 in a dotlike paranuclear pattern and negative for cytokeratin 5/6, human melanoma black 45, and leukocyte common antigen. Two weeks after the punch biopsy, the lesion noticeably decreased in size, and within 8 weeks of the biopsy the tumor had completely resolved with no further intervention. Regression of Merkel cell carcinoma (MCC) is a very rare event, with as few as 30 cases reported. The mechanism of this phenomenon remains unclear; however, T-cell-mediated immunity and apoptosis appear to play a major role.