Extramammary Myofibroblastoma in the Axilla of a Male Patient: A Case Report and Literature Review

Abstract

Mammary type myofibroblastoma in an extramammary location is an extremely rare benign lesion. The site involved is usually along the embryonic milk line with the inguinal/groin region as a common location. Here we report a case of such lesion in an old man who presented with a painless mass in the right axilla. Histologically the lesion was comprised of loosely distributed bland spindle cells in a pseudoangiomatous background. No cellular atypia or mitosis was identified.  Immunohistochemistry showed the spindle cells were immunoreactive to CD34, ER, and Bcl-2, but negative for desmin, cytokeratin, S-100, CD99, PR, CD21, and CD23. Ki-67 proliferative index for the spindle cells are very low.  A diagnosis of extramammary myofibroblastoma was rendered after multiple extramural expert consultations. The uniqueness of this case includes: 1) pseudo-angiomatous and loose stroma background with on obvious interspersed collagen bundles; 2) negative for desmin, which is usually positive for this type of tumor; and 3) positive for Bcl-2, which has never been reported. Comparison of this entity with spindle cell lipoma at genetic level and a literature review were also conducted.