cutaneous squamous cell carcinoma ( scc ) is derived from suprabasal epidermal keratinocytes and is very commonly encountered in clinical practice . it exists in many morphological forms , including keratinizing , non - keratinizing , clear , acantholytic , spindle and basaloid subtypes . the first case was reported by carmer and heggeness , but very few cases have been reported to date [ 2 , 3 , 4 , 5 ] . here , we report a case of signet - cell cutaneous scc arising on the back of a finger of an elderly male patient . physical examination revealed a 31  21 mm , reddish - brown , erosive macule on the back of the left fourth finger ( fig . 1a ) . medical imaging , including pet / ct , could not detect any other neoplastic lesions on the body . a biopsy taken from the lesion showed a thickened epidermis with parakeratosis , but no granular layer . notably , numerous signet - ring cells with crescentically compressed nuclei were seen extending to the cellular border ( fig . based on these findings , a histological diagnosis of solar keratosis , which was expected to advance to scc , was made . the lesion was therefore excised with a 5-mm margin and the wound was covered by a skin graft . histological examination of the whole tumor revealed irregular masses of proliferating tumor cells with invasive , atypical epidermal keratinocytes . the border of the lesion showed focal parakeratosis and a loss of normal epidermal stratification . signet - ring cells were present , both at the border and throughout the tumor ( fig . immunohistochemistry revealed that the tumor cells were negative for ck20 , carcinoembryonic antigen , vimentin , hmb45 , melan a and desmin . the patient has been monitored for 3 years , but no recurrence has been noted to date . signet - ring cells are cells in which the nucleus is crescentically compressed to the cellular border , resulting in a signet - ring appearance . this cell type is more commonly found in mucinous gastric carcinoma , although it is also present in a variety of other neoplasms including breast and pancreatic adenocarcinoma , leiomyosarcoma , liposarcoma and lymphoma . in skin tumors , the presence of signet - ring cells is indicative of metastatic adenocarcinoma , although these cells are only rarely found in some cutaneous neoplasms including scc , basal cell carcinoma and mycosis fungoides . signet - ring cutaneous scc is thus a very rare lesion and , as far as we know , only 4 cases have been described in detail [ 1 , 2 , 3 , 4 ] ( table 1 ) . in addition , one dermatopathologic report focused on the presence of signet - ring cells briefly described in clinical data of 6 cases . interestingly , in these reports , the skin lesions occurred exclusively in the head and neck area with 3 cases of a lesion on the forehead and the others on the neck , upper lip , canthus , cheek , temple , ear and frontal scalp . this suggests that the development of signet - ring cutaneous scc might be related to ultraviolet light exposure . this case involved a skin lesion on the back of the finger and is thus the first reported case of signet - cell cutaneous scc that did not arise in the head and neck area . a number of skin tumor types are known to occur more frequently in the head and neck area and these tumors are not always associated with actinic damage . it is also well established that some chemicals , scar formation and immune suppression are involved in the pathogenesis of cutaneous scc . the location of this lesion on the back of the finger , together with the histological findings compatible with actinic keratosis , support the hypothesis that the development of signet - ring cutaneous scc is related to ultraviolet light - induced damage .
a variety of pathologic variants of cutaneous squamous cell carcinoma ( scc ) has been reported , and the signet - ring variant of cutaneous scc is extremely uncommon . 
 we reported an 83-year - old man with signet - ring scc arising on the back of the finger . as far as we know 
 , only 4 cases have been described in detail , and one dermatopathologic report focused on the presence of signet - ring cells briefly described in clinical data of 6 cases . 
 interestingly , in these reports , the skin lesions of 10 cases occurred exclusively in the head and neck area . 
 this case involved a skin lesion on the back of the finger and is thus the first reported case of signet - cell cutaneous scc that did not arise in the head and neck area . 
 the location of this lesion , together with the histological findings compatible with actinic keratosis , support the hypothesis that the development of signet - ring scc is related to ultraviolet light - induced damage .