Diagnostic accuracy of immunohistochemical markers in differentiation between basal cell carcinoma and trichoepithelioma in small biopsy specimens

Differentiation of Basal Cell Carcinoma and Trichoepithelioma: An Immunohistochemical Study

ABSTRACT

Basal cell carcinoma (BCC) is the most common malignancy of the skin. It is an epithelial neoplasm with origin in the precursor cells of the interfollicular epidermis. Even though it has low metastatic potential, delay in management may lead to local destruction and morbidity. In contrast, trichoepithelioma (TE) is a benign tumor originating from the outer root sheath of the hair follicle. Similar to BCC, TE tends to affect the head and neck region. Both neoplasms may exhibit clinical and histopathological similarities, making them prone to misdiagnosis. Multiple immunomarkers have been used to distinguish among these entities, but so far, no single agent or combination of agents appear to be neither sensitive nor specific enough to differentiate between them. This study was divided into 2 parts. First, 17 cases of BCC and 14 cases of TE were stained with androgen receptor and bcl-2. Then, 27 cases of borderline/equivocal of BCC and 13 cases of borderline/equivocal TE were stained with the same protocol. Sensitivity and specificity were calculated for each individual immunomarker and for the combination of them. Androgen receptor positivity was 100% specific for BCC and borderline/equivocal BCC, whereas bcl-2 diffuse staining pattern demonstrated a sensitivity of 82.4% for BCC and 88.9% borderline/equivocal BCC. When both immunomarkers were combined, the sensitivity for BCC decreased (70.6%) but the specificity remained high (100%). Similarly, the sensitivity for borderline/equivocal BCC was 55.6%, whereas the specificity was 100%. Although moderately sensitive, combining both immunomarkers showed an excellent specificity to discriminate between BCC and TE.

Androgen receptor expression in epidermal and adnexal tumours

INTRODUCTION

Androgen receptor (AR) immunohistochemistry is used in general pathology and in dermatopathology, particularly for sebaceous tumours. The goal of this study was to quantify AR expression in benign and malignant epidermal tumours and adnexal tumours.

METHODS

We studied AR expression in 301 skin lesions using standard immunohistochemistry and compared 10 trichoblastomas, 10 sebaceomas and 10 hidradenomas using 5 markers (cytokeratin 7 and 8, PHLDA1, BerEp4 and AR).

RESULTS

The rates of AR expression were: 22% in basal cell carcinomas, 3% in squamous cell carcinomas, 92% in sebaceous tumours, 10% in follicular tumours and 22% in sweat gland tumours. Benign sebaceous tumours were AR+ in 97% of cases. Only 12% of sebaceous carcinomas showed no AR staining. The immunohistochemical profiles of the comparative study were as follows: sebaceoma: AR+, CK7-, CK8-, PHLDA1-, BerEp4-; hidradenoma: AR-, CK7+, CK8+, PHLDA1+, BerEp4+; trichoblastoma: AR-, CK7-, CK8-, PHLDA1+, BerEp4+.

DISCUSSION

AR staining was positive in 92% of sebaceous tumours, including sebaceomas, in some cases indicative of Muir-Torre syndrome. AR staining is therefore highly sensitive for the diagnosis of sebaceous tumours, but it is non-specific and is best used in combination with other antibodies, notably anti-CK8 and PHLDA1, particularly to distinguish sebaceoma from hidradenoma or trichoblastoma.

Basaloid tumors arising from seborrheic keratosis: Malignant basal cell carcinoma or benign basaloid follicular hamartomatous proliferation?

BACKGROUND

Basaloid tumors arising from seborrheic keratosis (SK) that resembled basal cell carcinoma (BCC) were infrequently observed in our patients. They also exhibited morphologic features similar to those of trichoblastoma or basaloid follicular hamartoma.

METHODS

We retrospectively collected cases of SK with basaloid tumors from 2001 to 2017. Ten cases of BCC, five of nevus sebaceus with trichoblastoma, five of trichoblastoma, and five of trichoepithelioma were included as controls. Tumor-associated antigens Bcl-2, CD10, PHLDA1, and CK20 were tested. Antigenic markers CD34 and CD10 were used to analyze peritumoral stroma features and Ki-67 and pHH3 to measure the mitotic activity.

RESULTS

Ten cases of SK with basaloid tumors were found and all located in non-sun-exposed areas, including five men and five women, with a mean age of 61 years. A distinct PHLDA1 staining was not observed. The staining patterns of basaloid tumor lobules associated with SK were similar to the benign control group. Bcl-2 staining in the tumor lobules was mostly negative. Peritumoral CD10 stain and CK20-positive Merkel cells in the lobules were observed and the mitotic counts were low.

CONCLUSION

Basaloid tumors arising from SK are not always BCC. They were all benign follicular hamartomatous proliferation in this case series.