Cutaneous Squamous Cell Carcinoma – Overview

Squamous cell carcinoma (SCC) is defined by the World Health Organisation as ‘a malignant neoplasm of epidermal (and mucous membrane) keratinocytes in which the component cells show variable squamous differentiation.’

 

Most SCCs appear on the areas of the skin which get the most sun exposure though this is not the only place which the can arise. SCCs can also arise on mucosal areas such as on the lip. Patients who have a pale complexion and those who do not tan readily are at a greater risk. SCC is very uncommon in the Black population.

The most important causative agent is sun exposure, more correctly UVB radiation. Others factors that have been incriminated include human papilloma virus (HPV) infection, ulcers, immunosuppression and radiotherapy. Patients with organ transplants are also at a greater risk. SCC can be fatal in some cases (most commonly found in Australia) giving rise to the notion that sun exposure, which causes DNA damage and also suppresses the skin immune system, plays a lead role in the cause of aggressive SCCs. 

As sun exposure is the major cause factor of SCC, it is no surprise that the forehead, ears, scalp, face, neck, back of the hands and lips are the most common places to find SCCs on the human body.

SCCs commonly appear as plaques/nodules with an elevated/indurated, crusty surface. The areas immediately surrounding the SCC show the typical signs of sun damage.

I have previously blogged about the prognostic factors of SCC, please click on the link to see more (Prognostic Factors of Cutaneous Squamous Cell Carcinoma)

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Solar Keratosis and Its Histological Subtypes

Solar keratosis is defined by the World Health Organization as ‘a common intraepidermal neoplasm of sun-damaged skin characterized by variable atypia of keratinocytes.’

Subtypes that are recognised are hypertrophic, atrophic, acantholytic, pigmented. lichenoid and bowenoid. All subtypes usually display the common features of hypogranulosis, parakeratosis along with keratinocyte atypia confined to the bottom two layers of the epidermis (basal and spinous). Below is some of the histological features commonly seen in the subtypes apart from the features mentioned above.

HYPERTROPHIC

This variant exhibits hyperkeratosis, acanthosis, papillomatosis, rete ridge elongation, telangiectasia and parakeratosis. The parakeratosis can be seen alternating with the hyperkeratosis.

ATROPHIC

This variant exhibits epidermal atrophy, basal epidermal budding with adnexal extension.

LICHENOID

This variant exhibits exocytosis, keratinocytic vacuolation, keratinocytic apoptosis, colloid bodies, band-like superficial dermal lymphocytic infiltrate and pigment incontinence.

ACANTHOLYTIC

This variant exhibits acantholysis (with possible extension down adnexae), suprabasal clefting and dyskeratosis.

PIGMENTED

This variant exhibits increased pigmentation of atypical keratinocytes with associated dermal melanophages.

BOWENOID

Although most pathologists consider this Bowen’s disease, some say bowenoid solar keratosis exhibits less than full thickness atypia and sparing of follicles.

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Basal Cell Carcinoma and It’s Histological Growth Types

Basal cell carcinoma (BCC) is the most common skin malignancy and it’s incidence is on the increase. Below is a description of the four main different histological growth types and what is features are associated with each of them.

Superficial

Superficial BCC presents as a scaly, reddish patch ranging in size from a few mm to over 100mm. Due to this clinical appearance there is often confusion with psoriasis. Superficial BCCs are most commonly found on the trunk and account for 10-30% of all BCCs. Histologically they are characterised by superficial collections of atypical basaloid cells projecting from the epidermis or from the sides of adnexal structures such as hair follicles or eccrine ducts. Due to the 2 dimensional processing of histology specimens most superficial BCCs appear multifocal but recent studies using digital imaging techniques show that the tumours nests are actually all interconnected. Truly multifocal superficial BCCs do occur but these are less common. 

Nodular

Nodular BCC most commonly appear as pale, pearly nodules often with macroscopically visible dilated blood vessels coursing over the top of the lesion. Nodular BCCs are most often found on the more sun exposed areas of the body (eg. face and neck). Histologically they are characterised by large, solid lobules of atypical basaloid cells exhibiting a peripheral palisade and often invading as far as the reticular dermis.  Other commons features including the classical BCC retraction artefact and tumour cystic degeneration.

Micronodular

Micronodular BCC most often present as slightly elevated/flat pale lesions. They are most commonly found on the back. Histologically, micronodular BCC appears as an invasive BCC with the tumour islands between 3-10 cells in width (approximately the size of a hair bulb). These smaller tumour islands commonly exhibit perineural invasion. Compared to nodular BCC, the excision margins of micronodular BCC can be more commonly underestimated leading to a higher recurrence rate. 

Infiltrating

Infiltrating BCC presents most commonly as an indurated, pale lesion whose clinical margins appear poorly demarcated. They are mostly found on the face and upper trunk. Histologically they appear as diffuse cords, strands, columns of atypical basaloid cells infiltrating deep into the dermis and that rarely exhibit a retraction artefact or peripheral palisade. Due to the highly diffuse infiltrating nature of this tumour perineural invasion is extremely common therefore recurrences are common. 

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