Rapid Evolution of a Squamous Cell Carcinoma In Situ to Locally Invasive With Perineural Involvement

We present a case of rapidly progressing squamous cell carcinoma in situ (SCCis) with progression to aggressive SCC. An elderly gentleman with multiple medical comorbidities presented with a left zygomatic tumor initially diagnosed as SCCis with adnexal extension on histology. After a period of approximately 10 weeks, the patient underwent Mohs micrographic surgery (MMS) with evidence that the tumor was now consistent with a well-differentiated SCC, with perineural involvement. MMS was stopped after two stages and the patient was sent to head and neck surgical oncology for further evaluation and management. It has been reported in the literature that 3–5% of SCCis will progress to invasive SCC; although the inciting event to cause such progression is unknown, it is thought that mutations in key oncogenes or tumor suppressor genes such as TP53 may play a role. In addition, as many as 31% of SCCis may have a component of invasive SCC that is missed on initial histology due to sampling bias. This case reminds us that sampling bias can occur during biopsy, SCCis can rarely progress to invasive SCC, and highly aggressive SCCs may prove to be therapeutically challenging requiring a multidisciplinary approach. J Drugs Dermatol. 2020;19(11):1110-1111. doi:10.36849/JDD.2020.5184.