they can occur anywhere on the skin and often appear as firm and well - demarcated dermal nodules . malignant degenerations within epidermal cysts are very rare [ 1 , 2 , 3 , 4 , 5 ] . case reports exist which emphasise the connection between basal cell carcinoma and epidermal cysts as both may arise from the infundibular portion of hair follicles [ 2 , 3 ] . here , we report the case of a basal cell carcinoma arising from an epidermal cyst . a man in his 50s presented to our department with a long history of a cystic lesion on the left shoulder which had rapidly grown in size over the previous 34 months . on physical examination , there was a firm , movable , well - demarcated , voluminous dermal nodule . on the basis of these clinical findings a working diagnosis of epidermal cyst was favoured , and the lesion was subsequently enucleated under local anaesthetic due to its progressive increase in size . macroscopically the cyst , which was 35 mm in diameter , was lined by a thick wall and contained a whitish lobulated nodule measuring 25 mm in its largest diameter ( fig . 1 ) . histology revealed a cystic basal cell carcinoma arising from the lining of an epidermal cyst ( fig . 2 ) . immunochemistry showed lack of expression of berep4 in the cyst 's squamous epithelium but strong positivity on the nodular portion ( fig . malignant tumours arising from epidermal cysts are rare [ 1 , 2 , 3 , 4 , 5 ] . the incidence of tumours originating from epidermal cysts is estimated at around 1% in the literature , with about 70% of them being squamous cell carcinomas and only about 10% of them being basal cell carcinomas [ 3 , 5 ] . the possible common origin from the infundibular portion of the hair follicle may explain the connection between basal cell carcinoma and epidermal cyst [ 2 , 3 ] . described a 55-year - old man with a cystic lesion on the back , which had been present for 20 years and had increased in size during the last year . a diagnosis of a basal cell carcinoma arising in an epidermal cyst was made after histological examination . ikeda and ono   reported the case of a 78-year - old man who presented with small papules on the upper eyelid present for 50 years . one cyst had grown rapidly and had been partially ulcerated for the last few years . both cases reported a lesion which had existed for many years but showed recent rapid growth , with histological examination favouring a diagnosis of malignant transformation . in addition , delacrtaz   reported the case of a basal cell carcinoma arising from an epidermoid cyst which had been present for several years in a 65-year - old woman . similarly in our case , due to the rapid change in size , the otherwise benign - looking lesion was excised and the histopathology report showed basal cell carcinoma arising from an epidermal cyst . given the lack of specific clinical parameters , a basal cell carcinoma arising from an epidermal cyst may not be recognised , and histological examination of these lesions plays an important role in arriving at a correct diagnosis and , consequently , appropriate management . policy restrictions implemented over the past few years in order to cut national health services costs , for so - called  benign skin lesions and the revision to the management of  clinically harmless cysts , with their referral to specialists and surgical excision having been discouraged , made the treatment of such cases a challenge for both general practitioners and dermatologists . this case , however , demonstrates that a history of progressive growth should prompt proper surgical excision and histopathological assessment even when a cyst might appear clinically benign .
malignant degeneration within epidermal cysts is very rare . 
 however , these lesions may not be recognised clinically , and histological examination plays an important role in arriving at a correct diagnosis . 
 hence , we believe that benign - looking cystic lesions with a history of progressive growth should be surgically excised and submitted for histopathological assessment .