Squamous Cell Carcinoma of the Skin
A malignant tumor originating from keratinocytes. It is characterized by squamous differentiation and an aggressive clinical course. Grossly, the neoplasm appears as a single endophytic or exophytic firm nodule, fixed to surrounding tissues and prone to ulceration.
Development of the carcinoma is promoted by areas of chronic trauma, actinic keratosis, burn scars, radiation dermatitis, and chronic dermatoses. Typical localization includes body areas exposed to active solar radiation (sunlight).
Histological Presentation: The tumor nodule is formed by haphazard aggregates of atypical cells with vacuolated, anaplastic nuclei and abundant cytoplasm. Numerous mitoses are observed, including atypical forms.
Key microscopic markers:
- Keratin pearls (corneal pearls) — rounded areas of hyperkeratosis in the center of tumor nests. Their abundance serves as a criterion for the degree of differentiation.
- Intercellular bridges — specific connections between squamous epithelial cells.
The tumor deeply invades the dermis, lymphatic vessels, and blood vessels. Special attention is paid to detecting perineural invasion, an indirect sign of which is lymphocytic aggregation around nerve bundles. Upon discovering such an infiltrate, the pathologist must perform deep tissue levels.
Prognostic Factors in Squamous Cell Carcinoma
The clinical course and probability of metastasis directly depend on several clinicomorphological parameters. Tumor thickness plays a key role:
- Less than 2 mm — the risk of metastasis approaches zero.
- 2 to 5 mm — the probability of metastasis is about 5%.
- Greater than 5 mm — the risk sharply increases to 20%.
Adverse factors also include patient immunodeficiency and a neoplasm diameter exceeding 2 centimeters (significantly increasing the likelihood of both recurrence and metastasis). The most critical parameters remain the degree of differentiation and the presence of vascular or perineural invasion.
Tumors with Appendage Differentiation
Neoplasms of this group are less common than epidermal carcinomas. Benign variants usually present at a young age and often represent developmental anomalies. Malignant appendage tumors are rare, slow-growing, and late-metastasizing; however, they feature asymmetric borders, areas of necrosis, pronounced cellular atypia, atypical mitoses, and invasive growth.
Among benign variants, sweat gland lesions are the most common:
1. Syringoma Most commonly diagnosed in women during puberty. It manifests as multiple symmetric firm papules 1–3 mm in diameter on the face (especially the eyelids), and less commonly on the trunk or scalp (causing localized alopecia). Microscopically, the tumor localizes in the upper and middle dermis. It consists of small cysts with a double-layered lining (outer layer of dark flattened cells, inner layer of light cuboidal cells). Basaloid cell cords resembling "tadpoles" in shape lie within the dense fibrous stroma between the cysts.
2. Hidradenoma The most common sweat gland tumor, occurring in middle-aged individuals. It presents as a firm-elastic solitary nodule (0.5–2 cm) on the scalp or neck. Histologically, the nodule is separate from the epidermis, forming cystic, ductal, and solid structures. Three cell types are distinguished: polygonal cells with hyperchromatic nuclei, clear cells with high glycogen content, and squamous cells forming "pearls".
Melanocytic Skin Tumors
Although melanocytic lesions originate from a different cell lineage, they are among the most common skin neoplasms and require differential diagnosis with epithelial tumors. They include:
- Congenital melanocytic nevi — present at birth, represented by well-circumscribed pigmented plaques or papules up to 1.5 cm. Microscopic examination reveals diffuse infiltration of the dermis by monomorphic melanocytes located along the epidermis and skin appendages.
- Dysplastic nevus (Clark nevus) — an atypical lesion characterized by a high risk of malignant transformation into melanoma. It can be either solitary or multiple.