pilar cysts are common , and benign lesions and malignant transformation in them is extremely rare . trichilemmal cyst or pilar cyst is defined as a cyst containing keratin and its breakdown products . it is usually situated on the scalp with a wall resembling external hair root sheath . it is seen mainly in the at middle age and is inherited in an autosomal dominant fashion . in this case report , we present a 55-year - old man with multiple giant pilar cysts that were present since childhood . one of the cyst on the chest was transformed to squamous cell carcinoma ( scc ) . a 55-year - old man was referred to us because of multiple cystic lesions located on the body , some of them measuring several centimeters [ figures 16 ] . these lesions were present since childhood , and during this period the patient had no complaint except cosmetic concerns . patient had ignored these lesions for many years until one of the lesions on the chest became ulcerated and then infected [ figure 5 ] . pathology of the lesion located on the chest showed neoplastic proliferation of the epithelial cells . pathology of the five other lesions showed a cystic lesion covered with stratified squamous epithelium without granular layer containing homogenous laminated keratin . mohs surgery was performed to excise large scc of the chest , and the site of operation was repaired by split - thickness skin graft technique . the patient visited every month for 1 year and during this period he showed no sign of recurrence in the operation site . also , no change was observed in the remaining pilar cyst of the patient and he is now followed every 6 months . one of the lesions on the chest was transformed to scc a closer view of the figure 1 close up of lesions on the trunk pilar lesions on the back of patient a close view of the scc showing large infected ulcer pilar cyst of the scalp pathology of the lesion on the chest showing squamous nests in well - differentiated scc pathology of pilar cyst showing trichilemmal pattern of keratinization ( 400 ) pilar or trichilemmal cysts contain keratin and its breakdown products , lined by a wall resembling the external ( outer ) hair root sheath . the patient had these lesions since childhood , although most patients with this lesions are affected in middle age . although pilar cyst are usually observed on the scalp , the giant cystic lesions of our lesions were scattered over the whole body . one of these lesions on the chest was transformed to squamous cell carcinoma that was excised using mohs surgery . according to our literature review , up to now the authors certify that they have obtained all appropriate patient consent forms . in the form the patient(s ) has / have given his / her / their consent for his / her / their images and other clinical information to be reported in the journal . the patients understand that their names and initials will not be published and due efforts will be made to conceal their identity , but anonymity can not be guaranteed . pilar cysts may rarely transform to scc and also may occur on many parts of the body . the authors certify that they have obtained all appropriate patient consent forms . in the form the patient(s ) has / have given his / her / their consent for his / her / their images and other clinical information to be reported in the journal . the patients understand that their names and initials will not be published and due efforts will be made to conceal their identity , but anonymity can not be guaranteed . pilar cysts may rarely transform to scc and also may occur on many parts of the body . the authors certify that they have obtained all appropriate patient consent forms . in the form the patient(s ) has / have given his / her / their consent for his / her / their images and other clinical information to be reported in the journal . the patients understand that their names and initials will not be published and due efforts will be made to conceal their identity , but anonymity can not be guaranteed . pilar cysts may rarely transform to scc and also may occur on many parts of the body .