a 70-year - old japanese man presented at our hospital with an asymptomatic , 20  30 mm irregularly shaped blackish , flat elevated plaque with a gray nodule in the periphery on his left lower leg ( fig .
the lesion had been present for 10 years and had recently enlarged , associated with bleeding .
dermoscopy revealed leaf - like areas , large blue - gray ovoid nests and multiple blue - gray globules ( fig .
basal cell carcinoma and malignant melanoma were listed as suspected diagnoses , and we performed an excisional biopsy of the tumor .
histopathological examination of the tumor revealed infundibular structures of the outer hair sheath in the center of the plaque , which consisted of three distinct parts ( fig . 2a ) .
the first part showed circumscribed massive aggregation of basophilic basaloid cells containing abundant melanin granules with peripheral palisading and retraction spaces ( fig .
this part of the tumor exhibited trichilemmal keratinization with squamous eddies , which were surrounded by a fibrous stroma ( fig .
the third part showed reticular aggregation of basaloid cells with small infundibular cystic structures in the papillary dermis ( fig .
the stromal part showed no fibrosis and abundant mucin deposition staining positive with alcian blue ( fig .
immunohistochemical staining revealed diffuse positivity for anti - bcl-2 in the first part ( fig .
3b ) , positivity only at the periphery of tumor nests in the second part ( fig .
microscopic examination of the tumor showed that it consisted of three distinct histological types : massive aggregation of basophilic cells was diagnosed as solid - type basal cell carcinoma , massive aggregation of clear cells with trichilemmal keratinization was diagnosed as proliferating trichilemmal tumor , and reticular small aggregations of basophilic basaloid cells in the papillary dermis were diagnosed as infundibulocystic basal cell carcinoma .
basal cell carcinoma with follicular differentiation in 1987 by tozawa and ackerman , and later in 1990 the tumor was proposed as a variant of basal cell carcinoma showing differentiation to infundibular cyst - like structures by walsh and ackerman .
clinically , the tumor presents as small papules / nodules , most commonly on the face .
characteristic histopathological features of the tumor are small symmetrical , circumscribed aggregations of basaloid cells containing numerous infundibular cyst - like structures .
infundibulocystic basal cell carcinoma is different from trichoepithelioma in that there are no follicular bulbs and papillae , no stromal fibrosis around the tumor , reticulated pattern of neoplastic cells , and abundant epithelial mucin . in the present case ,
anti - bcl-2 immunohistochemical staining was diffusely positive in portions of typical basal cell carcinoma and infundibulocystic basal cell carcinoma .
, bcl-2 is present within basal keratinocytes , mesenchymal cells of follicular papilla , clear cells of eccrine glands , melanocytes and lymphocytes .
anti - bcl-2 staining is useful for distinguishing between trichoepitheliomas and basal cell carcinoma , the former staining positively in the periphery of tumor nests , whereas the latter shows diffuse and widespread staining in all tumor nests .
basal cell carcinoma is a neoplasm proposed to be derived from epithelial germ cells , and infundibulocystic basal cell carcinoma is derived from the infundibulum of the hair follicle , whereas proliferating trichilemmal tumor is derived from the hair follicle isthmus .
there have been four reports of basal cell carcinoma arising with trichilemmoma without a pre - existing sebaceous nevus . taken together ,
the present findings suggest that basal cell carcinoma may be derived from hair germ cells , including the outer hair sheath and hair follicular infundibulum .
the authors report no conflicts of interest . there were no funding sources for this work .
 a 70-year - old japanese man presented at our hospital with an asymptomatic , blackish , irregularly shaped plaque with a gray nodule in the periphery on his left lower leg . 
 the lesion had been present for 10 years and had recently enlarged , associated with bleeding . 
 histopathologically , the tumor consisted of three distinct parts : the first part showed massive aggregation of basophilic basaloid cells with peripheral palisading and abundant melanin granules , and was diagnosed as solid - type basal cell carcinoma . 
 the second part showed aggregation of clear cells with squamous eddies , and was diagnosed as proliferating trichilemmal tumor . 
 the third part showed reticular aggregation of basaloid cells with infundibular cysts in the papillary dermis , and was diagnosed as infundibulocystic basal cell carcinoma . 
 we diagnosed this tumor as basal cell carcinoma with various forms of hair follicle differentiation , including differentiation into the outer root sheath . 
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