PD-1 inhibitor therapy of basal cell carcinoma with pulmonary metastasis

Basal cell carcinoma (BCC) may be challenging to differentiate from basaloid squamous cell carcinoma (bSCC), both clinically and histologically. BCC constitutes one of the most common tumours and metastatic behaviour is extremely rare. In contrast, bSCC is a rare entity with an increased propensity for distant metastasis. If these conditions develop into inoperable metastatic disease, the therapeutic alternatives are different, but the use of PD-1 inhibitors may be a valid option for both. Here, we report a case with complex histology with a component initially classified as bSCC with lung metastases and treated with the PD-1 inhibitor cemiplimab resulting in radiological and clinical responses. Re-examination of the lung biopsy using routine histomorphology in combination with immunohistochemical staining for cytokeratin 14, cytokeratin17 and BerEp4 has, however, revealed a histopathological pattern of BCC, which is in concordance with a similar analysis of the cutaneous primary tumour in the face that the patient underwent surgery for more than 5 years earlier.

Automated summary

Differentiating between basal cell carcinoma (BCC) and basaloid squamous cell carcinoma (bSCC) can be challenging both clinically and histologically. BCC is a common tumor with very rare metastasis, while bSCC is a rare entity with a higher propensity for distant metastasis. PD-1 inhibitors may be a valid therapeutic option for both types if they develop into inoperable metastatic disease.