Pseudoangiomatous Stromal Hyperplasia Research Articles

Contrast-Enhanced Breast Ultrasonography Reveals an Unusual Breast Tumor in a Male Patient With Gynecomastia

Pseudoangiomatous stromal hyperplasia (PASH), first described in 1986, is a benign breast lesion consisting of complex, anastomosing, slitlike pseudovascular spaces, which are either acellular or lined by slender, spindle-shaped cells. 1,2 The exact etiology of PASH is unknown. It usually presents as a breast mass, affecting women in their reproductive years. Pseudoangiomatous stromal hyperplasia has been reported in at least 25% of cases of gynecomastia. 2 Although PASH is a benign lesion, it has a propensity for growth over time and local recurrence after excision.3 Several small-scale studies already described the mammographic and gray scale ultrasonographic findings of PASH. 3,4,5 To our knowledge, the appearance of PASH on contrast-enhanced ultrasonography (CEUS) of the breast has never been described before. In past years, CEUS has been used increasingly in clinical practice to characterize indeterminate breast lesions. 6-14 In CEUS, a contrast agent consisting of a suspension of microbubbles is used to increase the blood echogenicity and to improve detection of slow and low-volume blood flow in microvessels (<5 μm). Because malignant breast tumors display neoangiogenesis that can be depicted by the contrast agent, it is believed that CEUS can be used to characterize breast masses and distinguish benign from malignant lesions. In this report, we describe the case of an elderly male patient with gynecomastia in whom conventional mammography and gray scale ultrasonography revealed a solid tumor in the left breast that was suggestive of malignancy. Additional workup of the lesion included CEUS of the breast with SonoVue (Bracco SpA, Milan, Italy) microbubbles to analyze tumor vascularization. On the basis of the CEUS findings, the lesion was down-staged to a benign breast lesion, probably a PASH. 6-13 After ultrasonographically guided biopsy of the lesion, histologic examination of the tissue confirmed the diagnosis. We describe the imaging characteristics of PASH on CEUS and provide an in-depth review of the literature.

A case of nodular pseudoangiomatous stromal hyperplasia (pash)

Pseudoangiomatous stromal hyperplasia (PASH) of the breast is a common microscopic lesion that is found at breast biopsy, and presents with proliferation of the stromal cells and slit-like pseudovascular spaces with endothelial-like spindle cells. In contrast, nodular PASH is relatively rare. We report here a case of nodular PASH with multiple palpable masses. A 49-year-old woman who had experienced gradual enlargement of her breasts for 13 years noticed an elastic but firm palpable mass in her breast. We were able to detect 7 masses in her right breast and 2 in the left. Ultrasonography and mammography demonstrated nonspecific findings, and FNA and CNB did not establish a diagnosis. An excisional biopsy was performed, and the pathological findings revealed nodular PASH. Eighteen months after the excisional biopsy, the size of the nodules and the whole breast had decreased remarkably. While the possibility of a change in the hormonal background or the influence of drugs was considered, we were not able to reach a single specific conclusion regarding the pathogenesis.

Imaging Characteristics of Malignant Lesions of the Male Breast

Most men referred for breast imaging have palpable lumps, breast enlargement, or tenderness. Most of the evaluated lesions are benign. Male breast cancer accounts for less than 1% of total male breast lesions. Differentiation between benign and malignant masses is critical because it alleviates patient anxiety and allows unnecessary procedures to be avoided. Clinically suspicious lesions referred for imaging should first be evaluated with mammography. In patients with questionable findings at mammography and for lesions that are difficult to image with mammography, ultrasonography (US) is often useful for further characterization. A discrete mass at mammography or US is suspicious for malignancy. The relationship of the mass to the nipple should be carefully assessed; an eccentric location is highly suspicious for cancer. Secondary signs occur earlier in male patients because of smaller breast size. Such signs include nipple retraction, skin ulceration or thickening, increased breast trabeculation, and axillary adenopathy. US of the axillary region is helpful for staging. At pathologic analysis, cystic lesions commonly demonstrate malignant findings; therefore, all cysts and complex masses should be worked up as potentially malignant lesions. Benign conditions that may mimic male breast cancer include gynecomastia, lipoma, epidermal inclusion cyst, pseudoangiomatous stromal hyperplasia, and intraductal papilloma.

Rapidly growing nodular pseudoangiomatous stromal hyperplasia of the breast in an 18‐year‐old girl

Pseudoangiomatous stromal hyperplasia (PASH) of the breast is a rare benign proliferation of mesenchymal stromal cells with irregular slit-like formations resembling angiomatous structures. In the majority of cases this lesion is a focal microscopic finding in breast biopsies performed for benign or malignant diseases. It may present in a pure diffuse or nodular form. The exact etiology and pathogenesis of this tumor-like lesion is still unknown, but a proliferative response of myofibroblasts to hormonal stimuli has been postulated. A large 12 x 9 x 3.5 cm rapidly growing nodular form of PASH of the breast in an 18-year-old woman is here described with clinical and histological findings. A possible hormonal etiology was indicated by elevated progesterone (three-fold) and decreased estrogen serum levels. Different diagnostic lesions, such as giant fibroadenoma and low-grade angiosarcoma, are discussed. To the authors' knowledge this is only the fourth case of nodular PASH of the breast reported in the English literature.

Fibrous Lesions of the Breast: Imaging-Pathologic Correlation

Fibroepithelial lesions of the breast are commonly seen in clinical practice. The masses are composed of a combination of prominent stroma and varying glandular elements. Fibroadenomas, benign lesions that derive from the terminal duct lobular unit, are the most common and are often identified at clinical examination or mammography as circumscribed masses. Benign mesenchymal tumors include focal fibrosis, pseudoangiomatous stromal hyperplasia, and fibromatosis or desmoid tumor. Phyllodes tumor, which is similar to fibroadenoma but has increased cellularity in the stroma, is typically benign but has malignant potential. Diabetic fibrous mastopathy, a stromal proliferation found in patients with juvenile-onset insulin-dependent diabetes, is a reactive fibrous lesion. Most of these lesions manifest as masses at clinical and/or mammographic examination. Some (eg, fibroadenomas) may be associated with calcifications. Except for fibromatosis and phyllodes tumor, fibroepithelial lesions need not be excised if the diagnosis is confirmed by the results of histologic analysis at percutaneous biopsy. To correctly differentiate between fibrous breast lesions that are benign and those that should be resected, the physician must be familiar with the correlated radiologic-pathologic findings in the various lesion types.

Nodular pseudoangiomatous stromal hyperplasia of mammary stroma in a case showing rapid tumor growth

Pseudoangiomatous stromal hyperplasia (PASH) is an uncommon benign breast disease that presents as a localized breast mass. Breast tissue affected by PASH is characterized by a dense, collagenous proliferation of mammary stroma, forming interanastomosing capillary-like spaces. The importance of this benign lesion lies in distinguishing it from low grade angiosarcoma. We report a case of a 38-year-old woman who presented with a rapidly growing breast tumor. She visited our hospital with a complaint of a painless right breast mass. Physical examination revealed a 3.6 x 2.2 cm, oval, elastic-firm, well-defined and easily movable mass. Mammograms revealed no discrete mass or calcifications. Sonographic examination revealed a 3.5 x 2.5 x 2.2 cm, oval, well-defined and homogenous hypoechoic mass without a cyst. A fine-needle aspiration sample of the breast mass showed some clusters of epithelial cells with small papillary structures and many scattered stromal cells with naked nuclei. Based on these findings, a provisional diagnosis of fibroadenoma was made and the patient was followed up. One year after the first visit, the mass enlarged rapidly and a follow-up mammogram revealed an 8.2 x 5.5 cm circumscribed mass without calcifications. Given the history of rapid growth of the mass, tumor excision was performed. The excised tumor was well demarcated and had a smooth external surface. Histologic examination revealed normal breast ducts and lobules, and specific proliferative epithelial changes were not seen. The lobular and duct structure of the breast parenchyma were separated by an increased amount of stroma. The fibrous stroma contained numerous anastomosing slit-like spaces. Isolated spindle cells appeared intermittently at the margins of the spaces resembled endothelial cells. Immunohistochemical staining showed that endothelial cells lining true blood vessels were positive for Factor VIII-related antigen, but the spindle cells were negative for Factor VIII. Pseudoangiomatous stromal hyperplasia was diagnosed.

Pseudoangiomatous Stromal Hyperplasia in Lesions Involving Anogenital Mammary-Like Glands

Pseudoangiomatous stromal hyperplasia (PASH), first reported in 1986, is nowadays a well-recognized change in the breast. We present three cases of lesions involving anogenital mammary-like glands demonstrating this feature. All patients were females (ages, 42, 43, and 53 years). Each presented with a solitary, 1.5- to 2-cm asymptomatic nodule. Locations included the perianal area, perineum, and labium majus. Histopathologically, one lesion was classified as low-grade phyllodes tumor, another as fibroadenoma, and in the remaining case PASH was found in the background of mild hyperplasia of anogenital mammary-like glands and substantial lipomatous metaplasia. In all lesions, PASH had an identical appearance to that in the breast, that is open, slit-like, often anastomosing channels devoid of erythrocytes and lined by discontinuous, often attenuated, inconspicuous cells without atypia or mitotic activity set in a hyalinized collagenous stroma. Quantitatively, PASH ranged in the above cases, forming a relatively small focus in the fibroadenoma and being quite extensive in the remaining two cases. In the phyllodes tumor, PASH areas exhibited focal hypercellularity and presence of myoid cells. In none of the cases were there cells with intranuclear inclusions or multinucleated cells. The lesions were surgically excised. Two patients with follow-up were disease-free at one and three years after the operation. As to our knowledge, PASH has not been previously described in the anogenital area, this feature seems to have been either overlooked or is genuinely rare in this location. It may occur in a preexisting lesion of anogenital mammary-like glands or may apparently by itself produce a clinically detectable lesion. The clinicopathologic features of PASH in the anogenital area seem to be identical to those in the breast.

Phyllodes Tumors of the Breast: The Role of Pathologic Parameters

We aimed to establish whether morphologic parameters were prognostically important in a large series of breast phyllodes tumors in Asian women. Of 335 phyllodes tumors diagnosed at the Department of Pathology, Singapore General Hospital, Singapore, between January 1992 and December 2002, 250 (74.6%) were benign, 54 (16.1%) borderline, and 31 (9.3%) malignant, based on histologic review of archival slides. Of the women, 43 (12.8%) experienced recurrences during the follow-up period. Recurrent disease was correlated with grade or classification (P = .028), stromal atypia (P = .016), stromal hypercellularity (P = .046), and permeative microscopic borders (P = .021). Multivariate analysis revealed that independent predictors of recurrence were pseudoangiomatous stromal hyperplasia (PASH) and margin status, whereby the presence of PASH and complete or negative margins reduced recurrence hazards by 51.3% and 51.7% respectively. The 7 women who died of disease during follow-up had malignant phyllodes tumor at the outset and experienced recurrences, and death was preceded by distant metastases.

Phyllodes Tumors of the Breast

We aimed to establish whether morphologic parameters were prognostically important in a large series of breast phyllodes tumors in Asian women. Of 335 phyllodes tumors diagnosed at the Department of Pathology, Singapore General Hospital, Singapore, between January 1992 and December 2002, 250 (74.6%) were benign, 54 (16.1%) borderline, and 31 (9.3%) malignant, based on histologic review of archival slides. Of the women, 43 (12.8%) experienced recurrences during the follow-up period. Recurrent disease was correlated with grade or classification ( P = .028), stromal atypia ( P = .016), stromal hypercellularity ( P = .046), and permeative microscopic borders ( P = .021). Multivariate analysis revealed that independent predictors of recurrence were pseudoangiomatous stromal hyperplasia (PASH) and margin status, whereby the presence of PASH and complete or negative margins reduced recurrence hazards by 51.3% and 51.7%, respectively. The 7 women who died of disease during follow-up had malignant phyllodes tumor at the outset and experienced recurrences, and death was preceded by distant metastases.

Mammary pseudoangiomatous stromal hyperplasia presenting as an axillary mass

Pseudoangiomatous stromal hyperplasia (PASH) of the breast is characterized by interanastomosing slit-like spaces lined with spindle-shaped cells in an abundant fibrous stroma. PASH is a relatively common incidental finding in the breast tissue removed for other reasons and rarely presents as a localized mass. The etiology of PASH is unknown, but hormonal factors are thought to be involved. Accessory breast tissue is subject to all pathologic changes found in the normal breast. We report a case of PASH that presented as a palpable axillary mass in a 43-year-old woman. To our knowledge, PASH has not previously been reported in the axillary accessory breast tissue. The spindle stromal cells in our patient showed immunophenotypic characteristics of myofibroblastic differentiation. Immunoreactivity for progesterone receptor was noted in the spindle cells. These findings support the hypothesis that endogenous hormones are involved in the development of PASH.

Aspiration biopsy of nodular pseudoangiomatous stromal hyperplasia of the breast: Clinicopathologic correlates in 10 cases

Nodular pseudoangiomatous stromal hyperplasia (PASH) of the breast is rare and often indistinguishable from fibroadenoma, clinically and on aspiration biopsy smears. We report our observations in 10 patients with PASH, evaluated by fine-needle aspiration (FNA) biopsy and core biopsy. We retrospectively reviewed the clinical, radiographic, cytologic, and histologic findings in 10 cases of pure nodular PASH. Ten patients with a presumed clinical and radiologic diagnosis of fibroadenoma underwent aspiration biopsy. The aspiration smears were diagnosed as fibroadenoma (4 cases), cellular fibroadenoma (1 case), schwannoma versus neurofibroma (1 case), fibrocystic change (3 cases; 2 with atypia), and "not specific for a lesion" (1 case). A diagnosis of PASH was not suspected in any case. A discrepant or imprecise cytologic diagnosis and/or the presence of dissociated spindle or epithelial cells, or cellular stromal fragments prompted a surgical excision in 7 of 10 patients (70%). The remaining 3 patients exhibited cytologic features of fibroadenoma and were diagnosed as such; however, surgical excision was recommended. Three patients underwent a subsequent core biopsy, with a diagnosis of PASH being made in 1 patient. FNA biopsy could not discriminate PASH from fibroadenoma in 4 of 10 patients (40%) or suggest a diagnosis of PASH in any case. On retrospective review, the finding of plump, spindle-shaped mesenchymal cells may be a cytologic clue to suggest a diagnosis of PASH.

Myofibroblastoma-like changes in fibro(stromo)-epithelial lesions of the breast: report of two cases

Sir, Apart from the well-known epithelial/stromal tumors of the breast, such as fibroadenoma and phylloides tumors, another group of biphasic lesions, showing a wide morphological spectrum on a common basic theme, does exist. These lesions have been variably termed “fibroepithelial tumors,” “hamartomas,” “fibroadenoma variants,” and “stromo-epithelial lesions” [1, 2, 3, 6]. The epithelial component usually features florid/sclerosing adenosis and ductal epithelial hyperplasia. The stromal component is usually composed of fibrous tissue in which mature lipomatous or cartilaginous or osseous components (hamartoma) may be occasionally encountered [6]. Although there is the possibility that stroma may also display a variable fibro/myofibroblastic and myoid differentiation [2, 3], to the best of our knowledge, myofibroblastomalike changes have not been reported in mammary fibroepithelial (hamartomas) lesions. Two women (25 years and 49 years) presented with two nodular breast masses, measuring 1.5 cm and 2 cm in greatest dimension, respectively, which were surgically excised with the pre-operative diagnosis of fibro-adenoma. Histologically, both surgical samples showed the typical features of the so-called “fibro-epithelial lesion,” being composed of an admixture of glandular and stromal component proliferation. The epithelial component consisted of florid and sclerosing adenosis admixed with foci of typical ductal hyperplasia. In both cases, the stroma was completely replaced by bland-looking oval to spindle cells with pale to slightly eosinophilic cytoplasm, arranged in short irregularly intersecting fascicles, interrupted by thick bands of brightly eosinophilic collagen (Fig. 1A, B). Sometimes cells were nested grouped and similarly surrounded by thick collagen bands (Fig. 1C). Cells had round to spindle-shaped nuclei with one or two visible nucleoli (Fig. 1B). These stromal changes were closely reminiscent of myofibroblastoma, typical type, of the breast. Immunohistochemically, the cells of both cases had a similar profile: diffuse and strong immunoreactivity to vimentin and a-smooth-muscle actin (Fig. 1D) and focal staining to desmin, CD34, and bcl-2 protein. No staining was obtained for calponin, h-caldesmon, and S100 protein. This immunophenotype, similar to what is observed in breast myofibroblastoma, is consistent with the fibro/myofibroblastic differentiation of stromal cells. It is well known that mammary stroma has the capability of modulating its cellular phenotype as well as its extracellular matrix components upon several pathological conditions. As tumors of mammary stroma (fibroadenoma, myofibroblastoma, solitary fibrous tumor, leiomyoma), fibro(stromo)-epithelial lesions are examples in which presumptive fibroblast-like mammary stromal stem cells may undergo multidirectional mesenchymal differentiation [4, 5]. This event may well explain the occurrence of a stromal fibromatosis-like fibro/myofibroblastic and/or myoid (leiomyomatous) differentiation in these lesions [2, 3]. The present study provides evidence that mammary stromal cells in fibro-epithelial lesions may also acquire morphological and immunohistochemical features similar to those observed in myofibroblastoma, supporting the hypothesis that such cells (interlobular? and/or intralobular?) are the precursors of myofibroblastoma. Similar myofibroblastoma-like stromal changes have been reported in the more cellular areas of “pseudoangiomatous stromal hyperplasia,” a lesion which is thought to be histogentically related to myofibroblastoma [7]. Although the characteristic slit-like spaces of this lesion are lacking in our cases, the possibility that we are dealing with a nodular, cellular variant of pseudoangiomatous stromal hyperplasia cannot be completely ruled out. G. Magro ()) Dipartimento G.F. Ingrassia, Anatomia Patologica, Universit di Catania, 95123 Catania, Italia e-mail: g.magro@unict.it Tel.: +39-95-3782024 Fax: +39-95-3782023

Observations on the Pathologic Diagnosis of Selected Unusual Lesions in Needle Core Biopsies of Breast

Pathologic diagnoses rendered on needle core biopsies of mammary lesions are primary determinants of further intervention. Such biopsies are being performed for an ever-widening range of diseases in an attempt to reliably and efficiently render a diagnosis. This review is intended to provide practical guidance to pathologists in dealing with selected unusual lesions encountered in these biopsies. Herein we offer advice on avoiding common diagnostic errors and on considering the relevant differential diagnosis of mucocele-like lesions, spindle-cell metaplastic carcinoma, adenomyoepithelioma, pseudoangiomatous stromal hyperplasia (PASH), collagenous spherulosis, myofibroblastoma, vascular lesions, and lymphoid infiltrates in the breast.

Pseudoangiomatous Stromal Hyperplasia of the Breast in Two Adolescent Females

The majority of breast lesions that present in adolescent girls are benign, with most being fibroadenomas. Rarely, a large and rapidly growing breast mass may be found to be the more recently described entity named pseudoangiomatous stromal hyperplasia (PASH). The pathogenesis of this lesion is attributed to hyperplasia of stromal myofibroblasts in response to hormonal stimuli. To date, PASH has rarely been described in adolescence. We describe the presentation of PASH in two adolescent patients. The first is a 12-year-old girl who found a mass in her left breast 3 months prior to presentation. An excision of an 11.5 x 10 x 3.5 cm lesion weighing 347 g was performed via breast-conserving incisions. The second patient is a 16-year-old girl who also had a rapidly enlarging left breast mass removed in a similar fashion. This mass measured 12 x 11 x 6 cm and weighed 460 g. Both tumors were noted to have a smooth capsule. Histologic appearance consisted of the typical features of PASH; fibrous stroma containing numerous anastomosing slit-like spaces; some compressed and others with discernible lumina. Both patients had complete excisions and have since not experienced recurrence. Each has had excellent cosmetic results with symmetrical breast development since their resection. Pseudoangiomatous stromal hyperplasia is a rare tumor that arises in the breast. These tumors may grow quickly and often are mistaken for fibroadenomas, phylloides tumor, or angiosarcoma. They must be resected with careful attention to resection around the capsule of the tumor with breast conservation as a goal. Long-term follow-up is necessary, as some have been reported to recur.

Pseudoangiomatous hyperplasia and stromal fibrosis of the breast

This presentation discusses two benign conditions of the breast—pseudoangiomatous stromal hyperplasia and stromal fibrosis. Once simply considered benign and relatively ignored by the breast imager, these lesions have assumed greater importance in the current era of image-guided core biopsies of the breast. The clinical and imaging presentations of these lesions will be discussed. A brief pathologic description will also be offered along with a differential diagnosis for these two benign entities. The importance of radiologic-pathologic correlation and management options will be discussed.

Biphasic lesions of the breast

Biphasic lesions of the breast are characterized by integral epithelial and stromal components. Determination of the stromal composition facilitates diagnosis. Lesions with predominantly specialized stroma include fibroadenoma and phyllodes tumor, and lesions with a mixture of nonspecialized and specialized stroma include fibroadenoma variant, hamartoma, and pseudoangiomatous stromal hyperplasia. Diagnostic difficulty may be encountered when a biphasic lesion has cellular stroma, raising the differential diagnosis of phyllodes tumor. Distinctive histologic features of phyllodes tumor include architectural frond formation, stromal cytological atypia, stromal mitotic activity, irregular gland dilatation, and morphologic heterogeneity. These histologic features contrast with those of other biphasic lesions.

Benign and malignant spindle cell lesions of the breast

Spindle cell lesions of the breast constitute a wide spectrum of benign and malignant proliferations. Myofibroblasts, normal cellular constituents of the mammary intra- and interlobular stroma, compose many of these lesions, which include reactive proliferations and benign or locally aggressive neoplasms. Because of its morphology, low-grade metaplastic spindle cell carcinoma, “fibromatosis-like” is also considered together with spindle cell lesions of the breast. Although certain of the lesions do not occur commonly, they represent diagnostic challenges. This review outlines the morphology of certain spindle cell lesions of the breast including pseudoangiomatous stromal hyperplasia, reactive spindle cell nodule, nodular fasciitis, myofibroblastoma, primary mammary fibromatosis, and low-grade metaplastic spindle cell carcinoma, “fibromatosis-like.” The differential diagnosis and diagnostic work-up of these lesions is discussed, and their clinical treatment and prognosis briefly summarized.

Pseudo-angiomatous stromal hyperplasia presenting as a breast mass: imaging findings in three patients

The authors review the mammographic, ultrasonographic and magnetic resonance (MR) imaging findings in each of three patients with a breast tumor corresponding to the characteristics of pseudo-angiomatous stromal hyperplasia (PASH). Imaging findings are indistinguishable from those of the more common type of fibroadenoma, and they are categorised as BIRADS type 3 lesions (probably benign lesions). Their benign condition and behaviour compared with other similar cases, allows the recommendation that surgical excision be avoided, and the patients monitored with periodic follow-up. The diagnosis can be confidently established by sampling with a breast core biopsy in the case of any doubt about whether the lesion is benign if the patient is anxious.

Evolving entities and changing concepts in breast pathology.

Among the evolving entities and changing concepts in breast pathology are those relating to columnar cell hyperplasia, pseudoangiomatous stromal hyperplasia, mucocele-like lesions, pleomorphic lobular carcinoma in situ, pseudo-Paget's disease of nipple, microinvasive carcinoma of breast, spindle cell metaplastic carcinoma, and minimal metastatic disease in axillary lymph nodes. Pathologists, as well as physicians involved in the management of breast diseases, need to be aware of these recent developments in breast pathology since the recognition and understanding thereof may have considerable clinical relevance.

Mammary Pseudoangiomatous Stromal Hyperplasia

To describe and reevaluate the fine needle aspiration cytology findings of pseudoangiomatous stromal hyperplasia (PASH) of the breast, with histologic, immunohistochemical and ultrastructural correlation. The authors reviewed the clinical features, fine needle aspiration cytology, histology and immunohistochemical results in all cases of mammary PASH encountered at Pamela Youde Nethersole Eastern Hospital, Hong Kong, during the 4-year period from January 1998 to May 2002. Ultrastructural examination was carried out in a selected example. The findings were compared with those in the literature. Four cases of PASH of the breast were encountered during the study period. The ages of the patients ranged from 34 to 56 years. One of them was a male presenting with gynecomastia. Only 2 cases had fine needle aspiration biopsies with a satisfactory cellular yield available for review. The cytospin preparations were of moderate cellularity and showed cohesive clusters of bland-looking ductal cells in a background of single, naked nuclei and some spindle cells containing fine chromatin and a discernible amount of cytoplasm. Occasional ductal cell clusters assuming a "staghorn" pattern, a feature commonly seen in fibroadenoma, were noted. Besides, there were scantly, loose and hypocellular stromal tissue fragments that contained spindle cells and occasional paired, elongated nuclei embedded in a fibrillary matrix. Histologic examination of the excisional biopsies confirmed the presence of PASH. It was characterized by many slitlike spaces rimmed by CD34-positive myofibroblasts/fibroblasts in a focally hyalinized stroma. Sometimes, ill-formed, fusiform aggregates of fibroblasts were also observed. Their fibroblastic nature was confirmed by electron microscopy. Fine needle aspiration cytology of PASH closely resembles that of fibroadenoma. Though subtle differences do exist, a definitive diagnosis is unlikely on the basis of the cytologic examination alone. PASH needs to be distinguished from borderline lesions, such as phyllodes tumor, and more sinister conditions, which sometimes have a similar cytologic appearance.