squamous cell carcinoma ( scc ) is the second most common nonmelanoma skin cancer after basal cell carcinoma ( bcc ) [ 1 , 2 ] . currently , diagnosis of a clinically suspect scc or bcc is confirmed by histological evaluation of a skin biopsy obtained from the clinically most suspicious part of the lesion . however , a biopsy only represents a small part of the lesion . especially in large lesions , this might result in a false - negative diagnosis or in missing a more aggressive part of the lesion [ 3 , 4 ] . furthermore , clinical evaluation of previously treated and/or large lesions can be difficult , and in such cases , it is hard to determine the most suspect area for a biopsy . reflectance confocal microscopy ( rcm ) is a noninvasive technique for in vivo imaging of the skin that allows evaluation of the total lesion area . it is known that rcm can visualize nonmelanoma skin cancer , melanoma and inflammatory skin diseases [ 6 , 7 ] . however , to the best of our knowledge , it is not described whether rcm might be used to select the location of a punch biopsy in a large and clinically indistinctive lesion . a 66-year - old patient with an erythematous lesion on the frontal part of the face was referred from the department of dermatology of the bernhoven hospital , oss , the netherlands . at this hospital , the lesion unfortunately , both treatments were ineffective . a punch biopsy after these therapies revealed the presence of a superficial bcc and , therefore , the lesion was treated with photodynamic therapy however , the lesion persisted and increased in size . the biopsies obtained after photodynamic therapy showed chronic inflammation and no residual tumor tissue . for further management , the patient was referred to the outpatient clinic of the department of dermatology , radboud university nijmegen medical centre , nijmegen , the netherlands . a clinical diagnosis of the erythematous lesion with a size of 2.3  2.1 cm was difficult due to the previously performed biopsies and treatments ( fig . treatment by surgical excision without prior establishment of the diagnosis was unfavorable due to the size and the location of the lesion . therefore , we used rcm for a noninvasive evaluation of the complete lesion to select the most suspect area for a biopsy . the major part of the lesion showed rcm features corresponding to normal skin or actinic keratosis . more importantly , one small part showed prominent aberrant features : a disrupted stratum corneum , keratinocyte atypia , spongiosis , increased capillary blood flow , flattening of the dermal epidermal junction , solar elastosis and a nest of atypical cells ( fig . histopathological evaluation of the biopsy showed the presence of a scc with an invasive growth of 0.9 mm . the lesion was excised and evaluation of the excision specimen showed multifocal actinic keratosis and two small foci displaying scc with an invasive growth of 0.8 and 0.5 mm . although it is known that rcm can be helpful for the diagnosis of nonmelanoma skin cancer , this case demonstrates the practical use of rcm as a tool to select the location for a punch biopsy in a large and clinically indistinctive lesion . in this case , the foci displaying scc were only a small part of the total lesion area . without rcm imaging prior to the biopsy , rcm allows evaluation of the total lesion area , which might reduce sample errors and delay in accurate diagnosis and treatment of large or clinically indistinctive lesions .
reflectance confocal microscopy ( rcm ) is a noninvasive technique for in vivo imaging of the skin that allows evaluation of the total lesion area . 
 this case report about a 66-year - old patient with a clinically indistinctive , previously treated erythematous lesion on the frontal part of the face demonstrates the use of rcm to select the proper biopsy location .