Squamous Cell
Carcinoma.

SCC is a major type of skin cancer.

What is SCC (Squamous Cell Carcinoma)?

SCC is the second most common type of non-melanoma seen in the skin cancer clinic in Australia (after BCC). Squamous Cell carcinoma is a cancer of keratinocytes which are the cells found in the thin top layer of the skin called the epidermis.

This article refers to “Invasive SCC.” The other type of SCC is an Intraepithelial Carcinoma (IEC). The appearance and treatment of invasive .v. IEC are different. The cancerous cells of an invasive SCC have spread into the dermis of the skin whereas the cancerous cells of an IEC remain in the epidermis (uppermost layer).

Who gets them?

Invasive SCC usually occurs after the age of 40 and usually develops in a pre-existing Solar Keratosis. They usually occur in sun exposed areas, especially the head and neck. SCC is around 3 times more common in men than women.

Invasive SCC is unlike a BCC because an SCC may occasionally develop into a secondary cancer.

What does SCC look like?

Naked Eye

SCC typically has at least one these features:

Fast Growing nodule
Ulceration
Feels Firm
Pain or Tenderness to touch
Raised, red and scaly (redness around the base can be a useful clue)

The appearance of an early SCC is similar to that of a thick (Hypertrophic) Solar keratosis. With further growth, an invasive SCC will typically be elevated and scaly. At this point, the base will be red and feel firm. A keratoacanthoma may look very similar.

Sometimes, invasive SCC is not scaly and may look like a nodular melanoma. Dermoscopy is very helpful although a biopsy will be required to make the final diagnosis & ensure the lesion has been removed. The type of solar keratosis that looks like an SCC is a “hypertrophic solar keratosis.”

Gallery of SCC

Treatment for SCC

What is the treatment of SCC?

Invasive SCC will need to be surgically removed with a margin of clinically normal-looking skin around the lesion. The margin required will tend to be greater than for a BCC. The exact margin chosen is a judgment that takes into consideration the risk factors for aggressive SCC

It’s helpful to consider the risk factors for SCC recurrence in terms of risk factors before biopsy and risk factors from the pathology report.

The risk factors for a more aggressive SCC that are known prior to surgical excision are:

SCC found in these sites are more likely to re-occur: Ear or hair-bearing lip.
Being on immunosuppressive medication
Having previous treatment for that SCC
Larger SCC is more likely to re-occur after treatment (eg. more than 2cm in diameter)
Not being very rapidly growing (as SCCs do tend to grow rapidly, this is not that helpful a risk factor)

The standard excision margin is around 3-4mm, but that precise figure will depend on clinical features and patient preference.

Following excision with margins, will any further treatment (eg. surgery) be required? The risk factors in the pathology report for an aggressive SCC are:

Invading nerves in the skin (“Perineural invasion”) – up to 5% of SCC shows perineural invastion.
“Poorly differentiated” (see pathology report below) SCC.
SCC Invading deep into the skin (dermis).
unusual pathological variants (eg “spindle cells”).

The latest guidelines highlight the importance of the depth of an SCC. Depth is measured using the “Breslow thickness,” which is the distance from the top of the skin (almost) to the deepest level of The SCC. The Breslow thickness is also used to stage melanoma, and its use to help stage SCC is a recent development. A Breslow thickness of at least 2mm indicates an SCC that may be more aggressive.

Further treatment (Surgery) will often be required when the above pathological features are identified.

The excision margin required for SCC will tend to be greater than for a BCC

SCC Pathology Report

These are some of the key terms that may be used in the SCC Pathology Report.

The degree of differentiation of the cells is an important piece of information.

Atypical keratinocytes

Atpical means that the keratinocytes are not typical eg. the cells look glassy, and their nuclei look abnormal. Some divide by mitosis abnormally.

Keratinocytes extending into the dermis

The Keratinocyte cells do not look typical and they extend into the dermis. The keatinocytes clump together as island that are found in the dermis.

Keratinization

Keratin forms in excess amounts. This accounts of the scale. The keratin may found in cells or outside cells. When keratin is found in large amounts forms a keratin horn (which are also found with keratoacanthoma). A keratin horn is a visible projection of scaly skin.

Differentiation

The cells may appear the same as normal keratinocytes (well differentiated), not quite the same (medium differentiation) or very different (poorly differentiated). Poorly differentiated indicates that the tumour cells are dividing more rapidly and may require additional monitoring or further treatment.

Well differentiated SCC cells may produce quite a lot of keratin ie. scale.

Perineural Invasion

Perineural invasion (PNI) indicates invasion of nerve cells. Perineural invasion is more likely to be found in elderly people, and tends to involve the head and neck. They are found in around 5% of invasive SCC.

Perineural invasion is an important risk factor for aggressive SCC.

PNI involving nerves of greater than 0.1mm has a higher rate of recurrence and metastasis.

Breslow Thickness

Breslow thickness is the distance between the top of the skin and deepest area of the SCC.

The upper layer is fixed and is found at the top of the granular layer of the epidermis – this is very close to the surface of the skin.

A Breslow thickness of >2mm is a risk factor for a more aggressive SCC.