Extra-acral calcifying aponeurotic fibroma: a distinctive case with 23-year follow-up

Calcifying aponeurotic fibroma (CAP) is an unusual but well‐characterized soft tissue neoplasm that typically involves the digits of children and frequently recurs locally. This report describes a case from the subcutis of the lumbosacral region. A 26‐year‐old man initially presented at age 3 and developed three recurrences over a 23‐year period each at approximately 8‐year intervals (ages 10, 18, and 26). The microscopic findings in all recurrences showed a lobulated, poorly circumscribed proliferation of dense fibrous tissue containing epithelioid‐like fibro‐blasts, multinucleated cells, and islands of metaplastic chon‐droid differentiation with focal calcification. Despite origin from an unusual anatomic site, this case reported herein demonstrates the classical morphologic features and clinical history of CAT which showed little in the way of morphologic evolution despite 23 years of persistence. The clinical and histologic features helpful in distinguishing CAP from infantile fibromatosis and soft tissue chondroma are discussed.