# Uncommon Collision Tumors: Dermoscopic and Histopathological Features of Basal Cell Carcinoma Overlying Dermatofibroma

## TL;DR

This paper reports two rare cases where a skin cancer called basal cell carcinoma overlapped with a benign tumor called dermatofibroma, highlighting the importance of dermoscopy for accurate diagnosis.

## Contribution

The paper presents two new clinical cases of collision tumors involving basal cell carcinoma and dermatofibroma, emphasizing dermoscopic diagnostic criteria.

## Key findings

- Collision tumors of basal cell carcinoma and dermatofibroma are rare and challenging to diagnose.
- Dermoscopy is crucial for distinguishing these overlapping lesions and avoiding misdiagnosis.
- Accurate diagnosis ensures appropriate treatment and prevents incomplete excision.

## Abstract

Dermatofibromas (DFs) represent prevalent benign fibrohistiocytic tumors, typically manifesting as solitary lesions. In the majority of cases, the clinical presentation and dermoscopic and histopathological features of DFs adhere to a characteristic profile. However, DFs may exhibit atypical clinical presentations and, more commonly, histologic attributes, posing challenges in differential diagnosis. Both DFs and basal cell carcinomas (BCCs) are frequently encountered cutaneous lesions, each characterized by distinct clinical and dermoscopic features and microscopic morphology. The simultaneous occurrence of these two entities within the same lesion is rare. DFs have been documented to form collision tumors in conjunction with a spectrum of benign and malignant lesions, encompassing not only BCC but also balloon cell nevus, squamous cell carcinoma (SCC), and melanoma. Alterations in the epidermis overlaying a DF range from simple hyperplasia to the proliferation of basaloid cells. Accurate diagnosis, leading to the complete excision of the lesion, is contingent upon the recognition of dermoscopic criteria, precluding misinterpretation as a benign lesion. We present two cases of collision tumors comprising DF and BCC. This case report underscores the paramount importance of dermoscopy and adherence to dermoscopic criteria in the assessment of collision lesions and the diagnostic process related to cutaneous malignancies.