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Metastatic Basal Cell Carcinoma or Cutaneous Squamous Cell Carcinoma: Diagnostic Role of Genomic Tumor Sequencing

By: Emily Rhode
Posted: Wednesday, October 20, 2021

Certain metastatic basal cell carcinomas of the head and neck that are highly likely to metastasize are rare and therefore frequently misclassified as cutaneous squamous cell carcinomas. Analysis of the tumor’s genome may provide a way to help differentiate metastatic basal cell carcinoma from initially misdiagnosed metastatic cutaneous squamous cell carcinoma, according to a case series reported by Kylee J.B. Kus, BS, and Emily S. Ruiz, MD, MPH, of Harvard Medical School, Boston, and published in JAAD Case Reports. They concluded that because of the presence of a PTCH1 gene mutation in 73% of basal cell carcinomas, but not in cutaneous squamous cell carcinomas, genomic tumor analysis might be used to diagnose metastatic basal cell carcinoma correctly. 

In the first case, a 57-year-old man with chronic lymphocytic leukemia presented with infiltrative basal cell carcinoma. The patient received salvage intensity-modulated radiation therapy. After 1 year, a CT scan revealed a different tumor that, when biopsied, was found to be a cutaneous squamous cell carcinoma with basaloid features. A PET-CT scan showed osseous disease. A biopsy revealed carcinoma with basaloid features. Genomic profiling of a bone specimen identified a mutation of the PTCH1 gene.

In the second case, a 55-year-old man underwent wide local excision for recurrent basal cell carcinoma. After 5 years, lung nodules were discovered on CT, and histology suggested metastatic cutaneous squamous cell carcinoma. Genome sequencing revealed mutations in the PTCH1 gene, confirming metastatic basal cell carcinoma.

In the third case, a 66-year-old patient underwent Mohs micrographic surgery for basal cell carcinoma. After 2 years, a biopsy revealed an epithelioid neoplasm consistent with cutaneous squamous cell carcinoma. In addition, metastasis was discovered through PET-CT imaging. Consequently, genomic sequencing was performed, revealing a mutation in the PTCH1 gene and confirming metastatic basal cell carcinoma. 

Disclosure: The study authors reported no conflicts of interest.

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