Full thickness squamous atypia of the glans penis on a background of Zoon's plasma cell balanitis

Erythroplasia of Queyrat (EQ) or squamous cell carcinoma in situ of the glans penis developed in a 79 year old uncircumsised gentleman who had a six year prior history of biopsy proven Zoon's plasma cell balanitis (ZB) affecting the same site on the glans. Prior to the development of clinically evident EQ, the glans had been treated with topical pimecrolimus 1% for one month. The glans was subsequently treated with topical 5-flourouracil 5% for two weeks which resulted in clinical clearance.
EQ is obviously an important differential for penile plaques because of the potential for progression to squamous cell carcinoma, while ZB is generally regarded as benign. The differentiation can only be reliably made histologically.
There are other case reports of both EQ ( 1 ) and carcinoma of the penis ( 2 ) arising in patients with ZB, raising the question as to whether ZB may actually reflect a reaction to underlying pre-existing pathology or even a premalignant state.
The addition of topical pimecrolimus shortly before EQ became clinically evident in this patient is concerning in the light of recent concern regarding the carcinogenicity of topical calcineurin inhibitors ( 3 ).
This case highlights the importance of close clinical follow up of persistent penile inflammatory lesions and prompt biopsy of clinically suspicious areas as second and potentially more serious pathology may occur concomitantly.