Tissue of origin
The International Classification of Diseases for Oncology (ICD-O) system lists a number of morphological subtypes and variants of malignant squamous cell neoplasms, including:
Papillary thyroid carcinoma (code 8050/3)
Verrucous squamous cell carcinoma (code 8051/3)
Papillary squamous cell carcinoma (code 8052/3)
Squamous cell carcinoma (code 8070/3)
Large-cell keratinizing squamous cell carcinoma (code 8071/3)
Large-cell nonkeratinizing squamous cell carcinoma (code 8072/3)
Small-cell keratinizing squamous cell carcinoma (code 8073/3)
Spindle-cell squamous cell carcinoma (code 8074/3) It is also known as spindle-cell carcinoma, and is a subtype characterized by spindle-shaped atypical cells. Adenoid/pseudoglandular squamous cell carcinoma (code 8075/3)
Intraepidermal squamous cell carcinoma (code 8081/3)
Lymphoepithelial carcinoma (code 8082/3)Other variants of SCCs are recognized under other systems, such as keratoacanthoma. Other histopathologic subtypes
Erythroplasia of Queyrat
Marjolins ulcer is a type of SCC that arises from a nonhealing ulcer or burn wound. More recent evidence, however, suggests that genetic differences exist between SCC and Marjolins ulcer, which were previously underappreciated.One method of classifying squamous cell carcinomas is by their appearance under microscope. Subtypes may include:

Adenoid squamous cell carcinoma (also known as pseudoglandular squamous cell carcinoma) is characterized by a tubular microscopic pattern and keratinocyte acantholysis. Basaloid squamous cell carcinoma is characterized by a predilection for the tongue base. Clear-cell squamous cell carcinoma (also known as clear-cell carcinoma of the skin) is characterized by keratinocytes that appear clear as a result of hydropic swelling. Signet ring-cell squamous cell carcinoma (occasionally rendered as signet ring-cell squamous cell carcinoma) is a histological variant characterized by concentric rings composed of keratin and large vacuoles corresponding to markedly dilated endoplasmic reticulum.
TP63 staining is the main histological marker for Squamous cell carcinoma. In addition, TP63 is an essential transcription factor to establish squamous cell identity. Classification
Cancer can be considered a very large and exceptionally heterogeneous family of malignant diseases, with squamous cell carcinomas comprising one of the largest subsets. All SCC lesions are thought to begin via the repeated, uncontrolled division of cancer stem cells of epithelial lineage or characteristics. SCCs arise from squamous cells, which are flat cells that line many areas of the body. Some of which are keratinocytes. Accumulation of these cancer cells causes a microscopic focus of abnormal cells that are, at least initially, locally confined within the specific tissue in which the progenitor cell resided. This condition is called squamous cell carcinoma in situ, and it is diagnosed when the tumor has not yet penetrated the basement membrane or other delimiting structure to invade adjacent tissues. Once the lesion has grown and progressed to the point where it has breached, penetrated, and infiltrated adjacent structures, it is referred to as "invasive" squamous cell carcinoma. Once a carcinoma becomes invasive, it is able to spread to other organs and cause the formation of a metastasis, or "secondary tumor".