Clinical Dermatology Open Access Journal ISSN: 2574-7800 Congenital Primary Cutaneous Rhabdomyosarcoma of the Perineum with Mixed Histopathological Features and Unusual Expression of Smooth Muscle Actin: Report of a Case Clin Dermatol J Congenital Primary Cutaneous Rhabdomyosarcoma of the Perineum with Mixed Histopathological Features and Unusual Expression of Smooth Muscle Actin: Report of a Case Shabaka FH 1 , Abd-Alwadood FA 1 , Moftah NH 1 , Abdel-Halim MRE 2* , El-Nabarawy EA 2 and Kamel AM 1 1 Dermatology and Venereolgy Department, Al-Azhar University, Egypt 2 Dermatopathology Unit, Dermatology Department, Cairo University, Egypt *Corresponding author: Mona R.E. Abdel-Halim, MD, 108 Nile Street, Dokki, 12311, Cairo, Egypt, Fax: 0020237494428, Tel: 00201222874551; E-mail: abdelhalimmona@gmail.com Abstract Rhabdomyosarcoma (RMS) affecting the soft tissue of the perianal and perineal regions in children is uncommon and account for 2% of all rhabdomyosarcomas. Primary cutaneous presentation in this anatomical location is extremely rare. We report a 9-month-old female infant with a congenital primary cutaneous RMS presenting as a polypoidal exophytic mass in the perineum mimicking giant condyloma acuminatum (Buschke and Löwenstein tumor). Histopathological examination revealed a predominantly alveolar RMS with areas showing embryonal and pleomorphic features. In addition to expressing desmin and myogenin, the tumor cells also expressed smooth muscle actin. Keywords: Rhabdomyosarcoma; Soft Tissue; Visceral Organs; Tumors; Embryonal Introduction Rhabdomyosarcoma (RMS) is a malignant mesenchymal neoplasm that arises from mesenchymal precursors of striated (skeletal) muscles [1]. It typically arises in deep soft tissue or in visceral organs and thus seldom presents to dermatologists. It represents 53% of soft tissue tumors in the pediatric population [2]. Histopathologically, RMS includes three main types: embryonal (including botryoid, spindle and anaplastic variants), alveolar and pleomorphic with the first two types being the most commonly encountered types [3-5]. While the embryonal type tends to involve the soft tissues or viscera of the head and neck or the genitourinary tract, the alveolar type tends to affect the deep soft tissue of extremities [6]. Rare histopathological types of RMS include a distinctive spindle cell variant [7] and an epithelioid variant [8]. Compared to conventional RMS, tumors presenting in the skin are extremely rare and were found to represent 0.7% of all RMS cases collected at two large specialized institutes [9]. On the other hand, among all cases of cutaneous malignant solid tumors (primary or metastatic) studied in a Spanish pediatric dermatology department over duration of 14 years, cutaneous RMS represented 32% of the cases [10]. The skin can be involved by RMS either as a primary or a metastatic event. Primary cutaneous cases are very rare with less than 50 cases reported so far in the literature [11]. Cases are classified as primary cutaneous only after clinical and radiological exclusion of metastasis from RMS elsewhere or extension to the skin from an underlying deep soft tissue lesion. Primary cutaneous rhabdomyosarcomas (PC-RMS) tend to affect both children and adults with a bimodal age Case Report Volume 2 Issue 1 Received Date: January 07, 2016 Published Date: January 20, 2017 DOI: 10.23880/cdoaj16000109