Pathological classification of skin cancer

The pathological classifications of skin cancer are as follows:

(1) Squamous cell carcinoma: Histopathology shows that the squamous cells are not uniformly differentiated. Well-differentiated keratinocytes and poorly differentiated atypical squamous cells can be seen. The atypical epidermal squamous cells proliferate and can break through the basement membrane to grow invasively into the dermis and spread along the lymph nodes. The atypical squamous cell proliferates in different sizes. The cytoplasm is red-stained, rich in chromogens, and filamentous division phases can be seen. The more such cells there are, the more malignant the tumor is. Squamous cell carcinoma also has the characteristics of keratinization in pathology, that is, keratinized beads and squamous whorls can be seen in the tumor. Clinically, squamous cell carcinoma is divided into four grades according to the number of atypical squamous cells, the depth of cell infiltration, and the number of visible keratinized beads.

Grade I squamous cell carcinoma: The number of atypical squamous cells does not exceed 25%. The depth of infiltration does not exceed the level of sweat glands. The cancer cells vary in size and arrangement, and many keratinized beads can be seen. The boundary between the cancer cells and the surrounding tissue is unclear, and inflammatory reactions can be seen in the dermis of the surrounding tissue. This grade of squamous cell carcinoma rarely metastasizes.

Grade II squamous cell carcinoma: 25%-50% of the cells are atypical squamous cells. They invade the dermis and have a small amount of keratinized beads. The inflammation of the surrounding tissues is milder than that of grade I.

Grade III squamous cell carcinoma: Atypical squamous cells account for 50%-75%, and keratinized pearls are occasionally seen.

Grade IV squamous cell carcinoma: The tumor is almost entirely composed of atypical squamous cells without keratinized beads and more pronounced nuclear division. If the tumor cells are spindle-shaped and have no keratinization characteristics, immunohistochemistry, such as keratin staining, is required to assist in diagnosis.

(2) Basal cell carcinoma: Histopathology shows epidermal atrophy or ulceration, tumor cells are spindle-shaped or oval, with large, darkly stained nuclei and little cytoplasm. The boundaries between cells are unclear and they appear to be fused into a mass. The size, morphology, and staining of each cell are relatively consistent, with no obvious differences. There is no cell metaplasia, similar to basal cells, but the cells are arranged inconsistently. The interstitial tissue around the tumor cells proliferates and is arranged in a fence-like manner around the tumor cells. In HE-stained sections, part or all of the tumor can be separated from the surrounding stroma, resulting in a contraction gap. This phenomenon is caused by human factors during the preparation process. However, it is characteristic in basal cell epithelioma, which can help distinguish it from other tumors such as squamous cell carcinoma. In addition, the pathological manifestations of the four types of basal cell epithelioma are also different. In the case of pigmented basal cell carcinoma, melanocytes are scattered among the tumor cell masses, melanin granules are found in the cytoplasm, and there are many melanophages in the surrounding gaps. In the plaque-like basal tumor, the connective tissue proliferates significantly, and the tumor cells are arranged in cords in the dermis, with only one or two layers of cells. This type of lesion is often deeper. In superficial basal cell carcinoma, the epidermis often atrophies, and the subepidermal tumor cells invade the dermis downward in an irregular bud shape. Nodular ulcerative basal cell carcinoma has solid type, keratinized type, glandular type or cystic type in histological examination. Basal cell carcinoma can be divided into two major categories from a histological point of view: undifferentiated and differentiated. Undifferentiated tumors are called solid tumors, those differentiated into hair structures are called keratinized type (hair type), those differentiated into sebaceous glands are called cystic type, and those differentiated into apocrine or eccrine sweat glands are called glandular type. In some differentiated tumors, the tumors may show one or more differentiation tendencies.