phyllodes tumor ( pt ) is a rare fibroepithelial neoplasm accounting for less than 1% of all breast tumors .
benign pt ( bpt ) has hypercellular stromal fragments organized in leaflike patterns around benign epithelial / myoepithelial lined spaces .
standardized cytologic diagnostic criteria of bpt includes increased stroma over epithelium , highly cellular stromal fragments , presence of phyllodes fragments ( i.e. , abundant leaflike stromal fragments ) , myxoid stroma , and numerous single bare nuclei of spindle fibroblastic type .
diagnostic pitfalls of pt in fine - needle aspiration cytology ( fnac ) may be due to sampling error , high cellularity , ductal hyperplasia , paucity of stromal component , and occasional dissociation of epithelial cells .
occasionally , only epithelial components of pt is represented in smears and may be misdiagnosed as epithelial neoplasm , particularly tubular adenoma and carcinoma . here , we present a case of bpt diagnosed by excisional biopsy , but its fnac features were misleading due to predominance of the epithelial component showing a tubular adenoma - like pattern .
a 19-year - old female presented with an ill - defined mass in the left breast about ( 2.5  2 ) cm above the areola in the breast tissue .
on fnac , smear was cellular comprising of the predominance of benign ductal epithelial cells showing prominent tubular adenoma - like arrangement [ figure 1 ] and resetting arrangement [ figure 2a ] .
large branching sheets [ figure 2b ] and papillary clusters of ductal cells without a wavy or folded shape were seen as well .
because of diversity in cytological findings , various differentials were thought such as tubular adenoma , adenosis , papilloma , and fibroadenoma .
finally , it was cytologically reported as benign proliferative breast lesion with atypical / indeterminate features ( c3 category ) as per the cytologic categorization by the national coordinating committee for breast screening and the uk national breast screening program . as c3 category is a grey area in breast fnac diagnosis , further investigation such as excision biopsy
duct epithelial cell clusters showing tubular adenoma - like pattern in fnac ( h&e stain , 200 ) ( a ) duct epithelial cells in sheets showing rosette - like arrangement in fnac ( h&e stain , 200 ) ( b ) large branching sheets of bland epithelial cells ( h&e stain , 200 ) ( c ) duct epithelial cells showing focal apocrine metaplasia ( h&e stain , 400 ) excision biopsy specimen grossly consisted of two grey white soft tissue masses measuring 3.5 cm  3 cm  1 cm and 2 cm  2 cm  1 cm .
cut section showed grey white areas . on histology , a well - circumscribed biphasic neoplasm containing leaf - like , epithelial - lined papillary - like projections penetrating into cystic spaces with cellular stroma was seen .
though , cytological features of pt have been well characterized , the cytologic diagnosis of pt remains difficult .
this tumor is said to be underdiagnosed by the pathologists and undertreated by the surgeons .
thus , the preoperative diagnosis of this tumor becomes very important to allow correct surgical planning and to avoid reoperation ( wide local excision with at least 1 cm margin is currently the treatment of choice for bpt ) .
pt occurs in women aged 40 - 50 years , however , in asian countries pts may occur at a younger age ( average age , 25 - 30 years ) .
cytologic distinction of bpt from fibroadenoma is possible by noting large epithelial clusters longer than 1 mm , with a wavy or folded shape , in contrast to the small or medium - sized clusters with tubular , blunt - branching , or monolayered contours of fibroadenoma .
krishnamurthy et al . have observed that hypercellular stromal fragments with the presence of a significant proportion of long spindle nuclei ( > 30% ) is strongly indicative of pt , whereas the stromal cell nuclei in fibroadenoma tends to be short and oval and long spindle nuclei accounts for 10 - 30% .
however , in our case , all the abovementioned features were absent , which made cytologic diagnosis difficult .
standardized criteria for the diagnosis of bpt include at least two large stromal fragments , hypercellular fragments and moderate - to - large number of dissociated stromal cells .
predominance of epithelial elements over stromal elements and monotonous population of cells with tubular adenoma - like and rosetting pattern as seen in this case can mimic epithelial neoplasm .
large branching sheets of bland epithelial cells and focal apocrine metaplasia , seen here as well , closely mimics fibroadenoma .
presence of papillary - like clusters and acinar pattern could be the reasons to consider papilloma and adenosis as other differential diagnosis .
we conclude that if there is significant epithelial proliferation in bpt , a false diagnosis of epithelial neoplasm in fnac is possible and it is an important diagnostic pitfall .
so , very careful strict criteria should be used such as advised repeat fnac , cell block preparation , biopsy , or correlation with clinical and radiologic findings to improve preoperative diagnosis of bpt .
this will help in correct planning of surgical treatment , i.e. , wide excision with 1 cm margin .
 benign phyllodes tumor ( bpt ) is a biphasic neoplasm composed of bland stromal and epithelial elements . 
 cytologic diagnostic criteria of bpt , though documented in the literature , diagnostic pitfalls in fine - needle aspiration cytology ( fnac ) may occur due to sampling error , high cellularity , ductal hyperplasia , paucity of stromal component , and occasional dissociation of epithelial cells . here 
 , we describe a case of bpt diagnosed by histology in a 19-year - old female , where fnac features were inconclusive due to paucity of stromal component , predominance of tubular adenoma - like epithelial component , and due to the presence of other overlapping features with fibroadenoma . 