Squamous cell carcinoma of the skin
A malignant tumor originating from keratinocytes. Characterized by squamous differentiation and an aggressive clinical course. Macroscopically, the neoplasm appears as a single endophytic or exophytic dense nodule, fused with surrounding tissues and prone to ulceration.
Development of the carcinoma is promoted by areas of chronic trauma, actinic keratosis, burn scars, as well as radiation-induced and chronic dermatoses. Typical localization includes areas of the body exposed to active solar radiation (insolation).
Histological picture: The tumor nodule is formed by disorderly clusters of atypical cells with vacuolated, anaplastic nuclei and abundant cytoplasm. Numerous mitoses are noted, including pathological forms.
Key microscopic markers:
- Keratin pearls — rounded areas of hyperkeratosis in the center of tumor complexes. Their prominence serves as a criterion for the degree of differentiation.
- Intercellular bridges — specific connections between squamous epithelial cells.
The tumor deeply invades the dermis, lymphatic and blood vessels. Special attention is paid to detecting perineural invasion, an indirect sign of which is the accumulation of lymphocytes around nerve bundles. If such an infiltrate is found, the pathologist must perform deep serial sections of the tissue.
Prognostic factors in squamous cell carcinoma
The course of the disease and the probability of metastasis development directly depend on a number of clinical and morphological parameters. A key role is played by the thickness of the tumor nodule:
- Less than 2 mm — the risk of metastasis formation approaches zero.
- From 2 to 5 mm — the probability of metastasis is about 5%.
- More than 5 mm — the risk sharply increases to 20%.
Unfavorable factors also include the presence of immunodeficiency in the patient and a neoplasm diameter exceeding 2 centimeters (significantly increasing the likelihood of both recurrence and metastasis). The degree of differentiation and the presence of vascular or perineural invasion remain critical parameters.
Tumors with appendageal differentiation
Neoplasms of this group are less common than epidermal carcinomas. Benign variants usually manifest at a young age and often represent developmental malformations. Malignant appendageal tumors are rare, slow-growing, and metastasize late, but they are characterized by asymmetric borders, foci of necrosis, marked cellular atypia, pathological 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 dense 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 is localized in the upper and middle layers of the 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 skin of the head or neck. Histologically, the nodule is not connected to the epidermis and forms cystic, ductal, and solid structures. Three cell types are distinguished: polygonal with hyperchromatic nuclei, clear cells with a high glycogen content, and squamous cells forming "pearls".
Melanocytic skin tumors
Although melanocytic lesions originate from a different tissue lineage, they are among the most frequent skin neoplasms and require differential diagnosis with epithelial tumors. They include:
- Congenital melanocytic nevi — detected at birth, presented as well-demarcated 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.
Briefly: answers to topical questions
What are the histological variants of basal cell carcinoma of the skin?
The histological classification distinguishes the following variants of basal cell carcinoma of the skin.
- Basal cell carcinoma, NOS — tumor without additional specification.
- Nodular — nodular basal cell carcinoma.
- Superficial — superficial basal cell carcinoma.
- Micronodular form — micronodular form of the tumor.
- Infiltrative — infiltrative basal cell carcinoma.
- Sclerosing — morpheaform basal cell carcinoma.
- Basosquamous — basosquamous carcinoma.
- Pigmented form — pigmented form of basal cell carcinoma.
- With sarcomatoid differentiation — basal cell carcinoma with sarcomatoid differentiation.
- With adnexoid differentiation — basal cell carcinoma with adnexoid differentiation.
- Fibroepithelial — fibroepithelial basal cell carcinoma.
What are the microscopic criteria for Clark's dysplastic nevus?
The main microscopic criteria for Clark's dysplastic nevus include lentiginous melanocytic hyperplasia, cellular atypia, and stromal reactions.
- Dimensions — greater than 4 mm.
- Lentiginous melanocytic hyperplasia — irregular distribution of melanocyte nests along the dermo-epidermal junction.
- Clustering of melanocytes — localized in the area of epidermal rete ridges.
- Cellular atypia — moderately pronounced.
- Stromal reactions — fibrotic changes in the papillary dermis and perivascular lymphocytic infiltrates.
- "Shoulder" sign — the epidermal component exceeds the dermal component in extent.
- Confluence of melanocyte nests — formation of bridges between adjacent epidermal rete ridges in the epidermis.
To remember the histology: Squamous cell carcinoma builds "bridges" (intercellular bridges) and wears "pearls" (keratin pearls). Syringoma hides "tadpoles" (shape of cell cords) in the dermis.
Class and exam questions
Which histological sign indicates the degree of differentiation of squamous cell carcinoma?
The degree of hyperkeratosis, i.e., the number and maturity of "keratin pearls" in the center of the tumor cell nests.
What serves as a sign of possible perineural invasion in carcinoma?
The presence of pronounced lymphocytic infiltration around nerve bundles in the stroma requires additional sections to rule out tumor invasion into the nerve.
How to distinguish syringoma on microscopy?
Its main marker is the presence of small basaloid cords with a cystic space at one end, giving them the shape of "tadpoles" or "commas".
What cells form the basis of hidradenoma?
The tumor contains three types of cells: basophilic polygonal, clear glycogen-containing, and squamous epithelial (sometimes transitioning from one to another).
What else to study on this topic
- Features of basal cell carcinoma: stromal amyloidosis, mucinous cysts, and melanocyte proliferation.
- Intradermal melanocytic nevi: Mongolian spot, Ota nevus, and Ito nevus.
- Criteria for malignancy of Clark's dysplastic nevus.
- Clear cell variant of hidradenoma and its differential diagnosis.
- Granulomatous reaction upon rupture of syringoma cysts.
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