Use of HSP105 in the Differential Diagnosis of Basaloid Skin Tumors: A Study of 73 Cases.

Background: Basaloid skin tumors include subtypes of basal cell carcinoma (BCC) and the basaloid variant of squamous cell carcinoma (SCC). Due to their similarity in pathology and clinical presentation, their diagnosis is not straightforward. The aim of this study was to analyze the immunohistochemical expression of HSP105 in basaloid skin tumors, which include BCC, basosquamous carcinoma (BSC), metatypical basal cell carcinoma (MBCC), basaloid squamous cell carcinoma (BSCC), BCC with squamous differentiation as well as conventional SCC.

Methods: This retrospective study included 17 cases of BCC, 11 cases of BSC, 8 instances of MBCC, 10 cases of BCC with squamous differentiation, 8 cases of BSCC, and 19 cases of SCC. Their clinical characteristics were summarized, and the paraffin blocks of tumor biopsy specimens were collected for HSP105 immunostaining.

Results: In contrast to the BCC group, which stained predominantly negative, SCC stained diffusely positive for HSP105. BSCs showed some areas of HSP105 positivity with a transitional expression signature. HSP105 was only weakly positive in a few cases of MBCC. Although BSCC was stained positive for HSP105, the HSCORE was significantly lower than that of the classic SCC. In BCC with squamous differentiation, focal staining for HSP105 was only seen in the area of squamous differentiation.

Conclusion: There was a difference in immunohistochemical staining of HSP105 in basaloid skin tumors which helps in differential diagnosis. Differentiation between BCC, SCC, BSCC, MBCC, and BCC with squamous differentiation can be aided by immunohistochemistry using HSP105.