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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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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Non-melanoma skin cancer (NMSC) treatments

Below are the most common treatments available, plus a brief description, once a NMSC has been diagnosed (usually a basal cell carcinoma or a squamous cell carcinoma).

Surgical excision (standard) – the most common and preferred form of treatment. Good for nodular tumours with a sharply demarcated border. Has a high cure rate and is dependent on the closeness of tumour to the resection margin in regards to the pathology (ie. the closer the tumour is to the margin the more likely it is to recur). One let down is the bread loafing technique which results in only approximately 5% of the actual margins being visualised by the pathologist for assessment of complete excision.

Moh’s /  Moh’s Micrographic Surgery – form of treatment with the highest reported cure rate (~97-99%). This technique results in the entire peripheral margins and the deep margins being visualised and assessed for completeness of excision (this is why the cure rate is so high). One let down is the time-consuming nature of the technique and the specialised training that is involved.

Topical chemotherapy – the most common available topical chemotherapy agents include 5-fluorouracil (5-FU) and 5% imiquimod. Generally speaking 5-FU works by inhibiting DNA replication therefore the growth of the tumour and imiquimod works by modifying the local tumour immune response of the patient. Advantages include the non-invasiveness topical therapy. Disadvantages are that, used alone, they can only be used on superficial tumours and not invasive tumours. Experimentation of their use in conjunction with other treatments (eg. curettage then topical treatment, or topical use to reduce tumour size before excision) have resulted in reports of higher cure rates.

Curettage +/- Electrodissection – put simply the tumour is physically scrapped away then the treated area is exposed to an electrical current which results in the softening of the skin and the procedure is repeated until the treating physician is satisfied excision is complete. The curettage portion technique can be applied alone without the electrodissection. This technique is usually reserved for site which are cosmetically unimportant (eg back). The cure rate is dependent on how aggressive the technique is applied (ie. the more the aggressive the higher the cure rate) and the growth type of the tumour being treated (ie. the more invasive the tumour the lower the cure rate).

Cryotherapy – one of the older treaments for NMSC which involves treatment of the tumour most commonly with liquid nitrogen. Cure rate can be high but there is reduced tumour margin control resulting in a higher recurrence rate.

Photodynamic Therapy (PDT) – fairly new technique which involves applying a topical photosensitizer to the target tumour and then exposure of the target area to light. This results in the production of aggressive chemicals which damage the cell causing death. Disadvantages include the ineffectiveness on invasive and thicker tumours due to lack of light penetration, and high cost. Advantages include the non-invasiveness of the technique.

Radiotherapy – usually reserved for older patients or where the surgical removal of the tumour is not a viable option. Has a reported cure rate of approximately 80-95%. Tumours recurring after radiotherapy are generally more aggressive and can become radiotherapy resistant.

I welcome any comments or other therapies you have encountered.

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