DERMOSCOPY OF BASOSQUAMOUS CARCINOMA IN SITU
Authors: Voloshynovych M. S. , Girnyk G. Ye. , Tkach V. Ye. , Matkovska N. R. , Kozak N. V. 
Published: October 2022

Basosquamous carcinoma (BSC) is a rare, aggressive non-melanoma skin cancer with features that lie between those of basal cell carcinoma (BSC) and squamous cell carcinoma (SCC). BSC incidence is less than 2% of all non-melanoma skin cancers. A lot of controversies have been raised around the classification, pathogenesis, histologic morphology, biologic behavior, prognosis, and management of this tumor. Clinical differentiation from other BCC subtypes is difficult, although dermoscopic evaluation may provide some important clues. The dermoscopic pattern of BSC combines characteristics of both BCC and SCC including unfocused arborizing vessels, white structureless areas, keratin masses, ulceration or blood crusts, white structures, blue-gray blotches, and blood spots on keratin masses.

Biopsy and histologic examination remain the gold standard diagnostic method for BSC. The main published literature describes the presence of both BCC and SCC histologic characteristics with a transition zone between them. However, there is a certain controversy regarding how these features are arranged within the lesions. The correct histologic diagnosis of a BSC can be jeopardized when the biopsy is superﬁcial and not incisional. In this scenario, the lack of deep areas of the lesion in the sample may result in the incorrect interpretation of the tumor as a classic BCC.

Intraepidermal carcinoma (IEC) has long been considered a precancerous disease due to the fact that dysplastic and atypical cells are concentrated in the epidermis. They lack the fact of penetration through the basement membrane in order to become SCC. Modern practice refers to IEC as an SCC in situ localized extragenital.

We present a case of 63 years old patient. Erythematous macula with desquamation up to 1.3 cm in diameter, located on the chest, was revealed during the survey. At a non-polarised dermoscopy with fluid immersion there was a "gelatinous stroma" through which the dense network of multiple branched vessels is clearly visible, this is typical for BCC. But unfocused arborizing vessels were visible in some sectors, white structureless areas, keratin masses, blue-gray blotches, and blood spots on keratin masses that allow us to suspect a focal transformation in BSC. In the center, there were everal sectors filled with glomerular vessels, which is typical for IEC. The results of clinical and laboratory tests were within normal ranges. The dermoscopic picture combines changes that may point out BSC in the periphery and IEC in the central part of the formation. The fact of BSC worsens the patient's prognosis. BSC is characterized by an aggressive subclinical spread with higher rates of recurrence: 12–51%. We decided that immediate removal should be preferred. Taking into account the patient's age and accompanying pathology, a radical treatment method of removal by cryodestruction was chosen. During follow-up examinations, a normotrophic scar with a characteristic vascular pattern was formed on the patient's skin at the site of tumor removal. 

Conclusions. In our opinion, such a vascular pattern in the center of the lesion can testify to the picture of the transformation of BCC to BSC. At this stage, BSC, in some parts of the formation, is within the epidermis, and can probably be considered BSC in situ, which could be usefully explored in further research.