Authors: N. Frederick¹, N. Patel¹.

¹Dorevitch Pathology, Ballarat, Australia.  

Introduction: Trichoblastic carcinoma is a rare malignant adnexal neoplasm (1). They behave aggressively with a high rate of recurrence and metastasis (2), necessitating accurate and timely diagnosis.  

Case summary: Our case involves a 72YO male who had a punch biopsy of a preauricular lesion. Histology showed poorly differentiated squamoid cells with increased mitotic activity and AE1/AE3 positivity, resulting in a diagnosis of poorly differentiated squamous cell carcinoma (SCC). 

Histopathology of the resection specimen demonstrated a circumscribed solid-cystic mass with central papillary architecture and comedonecrosis. The cells were basaloid with focal moderate nuclear atypia and conspicuous mitoses, interspersed between bland eosinophilic stromal islands. IHC was positive for Ber-EP4 and p40. 

The case was referred for dermatopathologist opinion, which confirmed a diagnosis of trichoblastic carcinoma.  

Discussion: Trichoblastic carcinoma is a predominantly morphological diagnosis, with non-specific IHC staining and no current molecular techniques (3).

While the follicular component may be suggestive of SCC, the immunohistochemical profile diverges from the expected staining pattern with a positive Ber-EP4 and negative EMA. 

Other differentials include basal cell carcinoma (BCC), however the stromal component and lack of epidermal connection or retraction artefact precludes this.

Conclusion: Trichoblastic carcinoma is difficult diagnosis to make on small biopsy, due to the heterogenous nature of the tumour and non-specific IHC profile.

References: 

1. Goto, H. (2022). Current treatment options for cutaneous adnexal malignancies. Skin Cancer, 23, 736-748.

2.  Azevedo, C. et al. (2020). Trichoblastic carcinoma: A case report and literature review of an extremely rare and diagnostically challenging cutaneous malignancy of the hair follicel. SM Journal of Clinical Pathology, 4(4).

3. WHO. (2024). Trichoblastic carcinoma/carcinosarcoma. In D. Massi, & T. Brenn (Ed.), WHO Classification of Tumours. Retrieved from WHO Classification of Tumours: https://tumourclassification.iarc.who.int/chaptercontent/64/144