Collision tumor composed of mammary-type myofibroblastoma and eccrine adenocarcinoma of the vulva.

Collision tumors of the vulva are uncommon. Mammary-type myofibroblastoma is a rare benign tumor arising at extramammary sites with morphological and immunophenotypic features similar to the breast counterpart. Eccrine adenocarcinoma of the vulva is rare. The authors report here a true collision tumor containing a mammary-type myofibroblastoma with intermingling components of eccrine adenocarcinoma occurring in the vulva. An 80-year-old woman presented with a subcutaneous nodule in the vulva. The tumor was well circumscribed but unencapsulated. The mammary-type myofibroblastoma and the adenocarcinoma measured 4 cm × 3.5 cm × 1.0 cm and 1.5 cm × 1.2 cm × 0.8 cm, respectively. In the overlying superficial dermis there was an eccrine adenocarcinoma. It was composed of uniform basophilic cells arranged in tubules, solid nests, and cribriform growth patterns. The eccrine adenocarcinoma infiltrated the mammary-type myofibroblastoma in the submucosa. The soft tissue lesion revealed a spindle cell proliferation composed of fascicles of myofibroblastic cells embedded in a collagenous stroma with a predominance of mast cells. Interspersed thick hyalinized collagen bundles separated the fascicles. Immunohistochemically, the spindle cell tumor strikingly stained for both CD34 and desmin. To the best of our knowledge, this is the first case report of a vulva collision tumor composed of mammary-type myofibroblastoma intermixed with primary eccrine adenocarcinoma in the English literature.