Squamous cell carcinoma (SCC) of the skin is one of the three most frequent skin cancers with about 250,000 new cases diagnosed each year in the United States. Although most patients with the condition are cured, more than a tenth of them will eventually develop metastases. Treatment for small, superficial lesions is by electrodesiccation and curettage, while surgical excision or Mohs micrographic surgery are used for invasive disease.
A significant lifetime ultraviolet radiation exposure is the principal determinant of squamous cell carcinoma (SCC) and the disease appears most frequently in the older, fair-skinned population . Increased use of natural or artificial sunlight by the younger generation may be one of the reasons for the rising incidence of cutaneous squamous cell carcinoma (cSCC)  . Chronic skin ulceration and an immunosuppressed state are also predisposing factors for this malignant disease.
The carcinoma appears most commonly on sun-exposed areas, mainly on the head and neck. Changes are often present on the forehead, scalp, lip, and ears. The presentation is variable and the tumor could arise in the form of a plaque, nodule, or non-healing ulcer with scaling and crusting. The size is an important indicator for the risk of metastasis, as is the rate of growth and the state of differentiation of the cells. Growths larger than 2 cm metastasize more frequently than smaller ones  . Another factor influencing the rate of metastases is the location with the lips and ears among the most dangerous areas.
There are several forms of cSCC, which may range from in situ neoplasm to metastatic disease. Cutaneous SCC often develops from actinic keratoses which are very common, scaly and small precancerous lesions found on sun-exposed areas . Different studies report varying rates for actinic keratoses turning into invasive cSCC, while about a quarter of them will regress within a year . Actinic cheilitis, another precancerous lesion, appears on a lip as a fissure or dry patch, and sometimes develops into SCC. Squamous cell carcinoma in situ, in some cases called Bowen disease, is a precursor of fully developed cSCC. Invasive cSCC could spread locally and metastasize . The variant of SCC, Marjolin ulcer, can develop at the sites of chronic inflammation and has an over 30% metastasis and mortality rate   .
Conjunctival squamous cell carcinoma has a variable appearance. An unusual pterygium may indicate the presence of a tumor, hence all resected pterygia should undergo histologic examination .
A careful description of the appearance, location, and size of the tumor is essential. The gold standard for diagnosis is the histological evaluation. This method efficiently distinguishes cSCC from other skin conditions . Nevertheless, problems do arise, especially when the bioptic sample is too small . The biopsy must contain the full thickness of the diseased tissue, as well as adjacent normal skin for comparison. Excisional biopsy may be well suited for small lesions, but for larger lesions and those in esthetically and functionally important areas, incisional biopsy is performed as a base for a decision of definitive treatment.
Actinic keratosis contains atypical keratinocytes. It is classified according to the distribution of the atypical cells. In the first category (KIN I), the dysplastic keratinocytes are restricted to the lower third of the epidermis, whereas in higher categories they occupy an increasing thickness. In the KIN III category – which is the same as cSCC in situ - the atypical keratinocytes occupy all layers of the epidermis .
The classification of cSCC is according to the tumor-node-metastasis (TNM) staging system. This scheme incorporates the size of the tumor, the involvement of regional lymph nodes, and the absence or presence of metastases. An alternative scheme for nodal staging has been developed recently with good predictive power .
New methods for a noninvasive examination of skin lesions (dermoscopy, reflectance confocal microscopy, optical coherence tomography) have been developed . Computerized tomography (CT) and magnetic resonance imaging (MRI) are used to examine the extent of the disease.