Fine-Needle Aspiration Cytology of Pseudoangiomatous Stromal Hyperplasia of the Breast Philip C.W. Lui, M.B.B.S., 1 Bonita K.B. Law, F.R.C.S., 2 Winnie C.W. Chu, F.R.C.R., 3 Lai-Man Pang, F.R.C.R., 3 and Gary M.K. Tse, F.R.C.P.C., M.I.A.C. 4 * Pseudoangiomatous stromal hyperplasia (PASH) is an uncommon lesion usually found in premenopausal women. Histologically, it is characterized by complex, anatomosing, empty slit-like spaces in a dense collagenous stroma. These pseudoangiomatous spaces are lined by monomorphic spindle cells of myofibroblastic differenti- ation. Cytological features of PASH are rarely discussed and reported, and may pose diagnostic challenge to surgical patholo- gists. Two cases of PASH are reported with emphasis on the FNAC features and cytologic differentiation from other benign fibroepi- thelial lesions. Diagn. Cytopathol. 2004;30:353–355. © 2004 Wiley-Liss, Inc. Key Words: pseudoangiomatous stromal hyperplasia; PASH; fine- needle aspiration cytology Pseudoangiomatous stromal hyperplasia (PASH) is a be- nign breast mesenchymal lesion first described by Vuitch et al., 1 and is characterized by the presence of open slit-like spaces lined by bland spindle-shaped stromal cells in the breast stroma. PASH is usually asymptomatic, being dis- covered incidentally or may present as painless breast lump leading to further investigations by fine-needle aspiration cytology (FNAC) or excisional biopsy. Two cases of PASH were reported with emphasis on the FNAC features and cytologic differentiation from other benign fibroepithelial lesions. The first patient was a 24-year-old woman with good past health who presented with a slowly enlarging left breast lump for 10 months. There was no pain or nipple discharge, and no enlarged axillary lymph nodes were noted. Ultrasound showed a 7.7 cm oval mass with well- defined margin. Mammography showed a medium- density opacity devoid of calcification or architectural distortion. The mass was biopsied and subsequently ex- cised. The patient was well after the excision. The second patient was a 50-year-old woman with good past health presented with a right breast lump for 10 months. There was no change in size, and no associated symptoms including pain, discharge, or axillary lymph node en- largement were reported. Ultrasound showed an oval mass 1 cm in size with well-defined border. It was excised and the patient was well after the excision. FNAC was done under ultrasound guidance with an 18 gauge needle. Mild suction was applied after the needle penetrated into the lesion. Two to three passes were made during the aspirate. The direct smears and the cytospin preparations made using Shandon Cytospin 3 centrifuged at 600 rpm for 5 min were stained with Papanicolaou and hematoxylin-eosin. Both aspirates showed low cellular- ity. There were small- to medium-sized clusters of ductal epithelial fragments devoid of branching, and a dual population of myoepithelial and epithelial cells were present (Fig. 1). Some epithelial cells showed mild de- gree of nuclear enlargement, consistent with mild hyper- plasia. Scanty small stromal fragments were also present. All of them were small in size relative to the epithelial fragments. Most of these stromal fragments showed low cellularity and demonstrated marked crush artifact of the stromal cells nuclei. Unaffected spindle cells were noted at the periphery (Fig. 2). These spindle cells have ovoid nuclei, open chromatin, occasional nucleoli, and scanty 1 Department of Pathology, United Christian Hospital, Hong Kong, China 2 Department of Surgery, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, Hong Kong, China 3 Department of Diagnostic Radiology and Organ Imaging, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, Hong Kong, China 4 Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, Chinese University of Hong Kong, Shatin, Hong Kong, China * Correspondence to: Gary M.K. Tse, F.R.C.P.C., M.I.A.C., Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, Shatin, NT, Hong Kong, China. E-mail: garytse@cuhk.edu.hk Received 12 May 2003; Accepted 30 October 2003 DOI 10.1002/dc.20028 Published online in Wiley InterScience (www.interscience.wiley.com). © 2004 WILEY-LISS, INC. Diagnostic Cytopathology, Vol 30, No 5 353