Multilocular mesothelial proliferation involving the skin of the umbilicus.

Multilocular mesothelial proliferation (MMP) is a rare lesion that mainly arises from the peritoneal mesothelium. Most often, it occurs in women of reproductive age, with a history of abdominal surgery, endometriosis, or pelvic inflammatory disease. We describe an unusual case of a 73-year-old woman affected by a large MMP, which involved the skin and presented clinically as a cutaneous mass. To the best of our knowledge, MMP involving the umbilicus has never been reported in a peer-reviewed literature.