- 1 Background
- 2 Overview of evidence (non-systematic literature review)
- 2.1 Cutaneous squamous cell carcinoma
- 2.2 Actinic keratoses (including Bowenoid keratosis)
- 2.3 Bowen’s disease (squamous cell carcinoma in situ)
- 2.4 Keratoacanthoma
- 3 Notes on the recommendations
- 4 References
The majority of cutaneous squamous cell carcinomas (cSCCs) are thought to arise from actinic (solar) keratoses (AKs). The age and body-site distribution is therefore similar to that of AK. A few develop from chronic ulcers or scars, sites of chronic radiation dermatitis or from infrared irradiation.
The risk of cSCC is higher among immunodeficient individuals. Immunosuppression for organ transplantation strongly predisposes to cSCC (see: Organ transplantation and other conditions associated with prolonged immunosuppression).
There is probably a histological continuum of keratinocyte dysplasia from AK to invasive cSCC (see: Pathology). The continuum includes Bowenoid keratosisactinic keratosis showing full-thickness atypia without dermal invasion and Bowen’s diseasecSCC in situ (also known as intra-epidermal SCC) (cSCC in situ, also known as intra-epidermal squamous cell carcinoma). Distinguishing between each of these may be difficult for the clinician.
All of these tumours produce keratin, manifested as crusting. It is not the crusting or horn formation that represents the tumour; it is the erythematous base. Thickening, induration or tenderness on gentle lateral pressure of an erythematous base is suggestive of dermal invasion (invasive cSCC). Poorly differentiated cSCCs may not produce large amounts of keratin.
Overview of evidence (non-systematic literature review)
Cutaneous squamous cell carcinoma
Clinical features (cutaneous squamous cell carcinoma)
Cutaneous squamous cell carcinoma typically begins as a tender erythematous papule or nodule. This may be surmounted by a variable amount of hyperkeratosis, some producing a keratotic horn. The lesion enlarges over a period of months and becomes increasingly tender. Recurrent ulceration and bleeding may develop. Some, particularly on the scalp and legs, may present as an ulcer without a pre-existing nodule or surrounding induration.
Accuracy of diagnosis of cutaneous squamous cell carcinoma
Experienced dermatologists working in a Queensland prevalence study achieved a diagnostic accuracy of 39%, considerably lower than the 59% found for basal cell carcinoma (BCC).
The clinical diagnosis of early cSCC is difficult, particularly distinguishing it from a hypertrophic AK. It is likely that many early cSCCs are treated with cryotherapy based on a clinical diagnosis of AK.
The course of a cSCC is generally one of progressive enlargement. Ulceration and bleeding become more likely as the lesion enlarges. A few will become locally aggressive with perineural spread. Large lesions have greater potential for metastasis, generally to regional lymph nodes.
Squamous cell carcinoma may be difficult to differentiate clinically from nodular BCC and amelanotic nodular melanoma. Pearliness, telangiectasia and islands of pigment are helpful features of BCC. Amelanotic nodular melanoma may show some light brown pigmentation. Excision and histological assessment may provide the only way to establish the diagnosis. Dermoscopy is a useful adjunct in this diagnostic process and is recommended, particularly when pigment is present.
The majority of squamous cell carcinomas are thought to arise from AKs, although the vast majority of AKs do not become cSCCs.
Certain cSCC subtypes, sites and other features are associated with a poor prognosis (Table 2).
Practice Point (cutaneous squamous cell carcinoma)
PP 4.2.1. If a skin lesion is initially considered to be an actinic keratosis, but it persists following cryotherapy, enlarges or becomes tender, it should be biopsied to investigate the possibility of cutaneous squamous cell carcinoma or other dysplastic lesions.
Actinic keratoses (including Bowenoid keratosisactinic keratosis showing full-thickness atypia without dermal invasion)
Actinic (solar) keratoses are usually found on the chronically sun-exposed sites of head and neck, dorsum of hands and forearms. They are generally multiple and may be very numerous or confluent. A Bowenoid keratosisactinic keratosis showing full-thickness atypia without dermal invasion may have a slightly thicker erythematous base than an AK (see: Pathology)
Actinic keratoses present as erythematous macules with superimposed hyperkeratosis. Hyperkeratosis may be gross enough to produce a keratotic horn but the erythematous base of the lesion remains macular and impalpable.
There is no underlying induration when the lesion is palpated and they are generally non-tender. Actinic keratoses may be symptomatic. A variety of sensory symptoms including pricking, burning and stinging may be felt with sun exposure or perspiration.
Pigmented AK may need to be differentiated from solar lentigines and lentigo maligna. The erythema associated with hyperkeratosis is the most helpful distinguishing feature of AK. Actinic keratoses are less well defined at the periphery than cSCC in situ and are also less well defined than seborrhoeic keratoses, which are not normally erythematous.
Thickening and tenderness on lateral palpation are signs that a AK may have developed into invasive cSCC.
Clinical courseOnly a small percentage of AK evolve into invasive cSCC. According to one estimate, the rate of malignant transformation is less than one in 1000 per year. Many cSCCs, however, evolve from AK.
Bowen’s diseasecSCC in situ (also known as intra-epidermal SCC) (squamous cell carcinoma in situ)
Classical Bowen’s diseasecSCC in situ (also known as intra-epidermal SCC) was originally described by John Bowen as scaling erythematous lesions in non-light exposed areas of skin. With the increasing use by pathologists of the term to classify any lesion with histology displaying full-thickness keratinocyte dysplasia (atypia) in the epidermis (cSCC in situ), ‘Bowen’s diseasecSCC in situ (also known as intra-epidermal SCC)’ is now also applied to tumours with this histological characteristic in light-exposed areas.
Classical cSCC in situ presents as a sharply defined, erythematous, round-to-oval hyperkeratotic plaque. The degree of hyperkeratosis may vary, with some lesions producing a keratotic horn. It has a predilection for the lower limbs, particularly in females, but lesions with this histology also occur in frequently exposed areas, such as the head and neck. Squamous cell carcinoma in situ is generally asymptomatic. The clinical history is usually of a longstanding, slowly enlarging lesion.
Bowen’s diseasecSCC in situ (also known as intra-epidermal SCC)-like lesions on non-sun exposed areas (e.g. the areola/breast or genitals), could be Paget’s disease.
Classical cSCC in situ may be distinguishable from psoriasis by its long history, though the clinical appearances may be very similar. Superficial BCC may be distinguished from cSCC in situ by less hyperkeratosis, a shiny surface and the pearliness that becomes apparent on stretching a BCC. Hypertrophic cSCC in situ may mimic cSCC and a biopsy is frequently necessary to distinguish this from invasive cSCC. Pigmented Bowen’s diseasecSCC in situ (also known as intra-epidermal SCC) may mimic superficial BCC or superficial spreading melanoma.
Classical cSCC in situ will generally enlarge very slowly and will appear to the patient as a stable lesion. The rate of transformation to invasive cSCC has not been established, but would appear to be low. If a lesion changes, it should be biopsied to excluded transformation to invasive disease.
Whether keratoacanthoma is a form of cSCC or a separate lesion is still under debate (see: Pathology of keratoacanthoma).
Many keratoacanthomas arise in association with AK, and the age and site distribution is similar to that of AK and cSCC. The chronically exposed sites of the head and neck, hands and forearms are most commonly affected, though multiple keratoacanthomas most often occur on the limbs, particularly the lower limbs. Occasionally it may occur in sites related to trauma, surgery or burns.
The most characteristic feature of a keratoacanthoma is its clinical course. These begin as a small papule that rapidly enlarges to form an erythematous nodule with a central keratotic plug. The lesion continues to enlarge over a period of 4–8 weeks, remains stable for a period as an asymmetrical, dome-shaped erythematous nodule with a central keratotic plug. It may reach a size of several centimetres in diameter.
Keratoacanthomas are typically exquisitely tender until regression is well established. The fleshy rim then begins to recede, exposing more of the central keratin plug until there is an erythematous collar surrounding a keratotic horn. The central keratin plug then falls out and the remainder of the lesion resolves, sometimes leaving a scar.
On occasion, a keratoacanthoma may develop soon after trauma or surgery.
They may be multiple.
Keratoacanthomas often undergo spontaneous resolution. Resolution generally occurs within 6–12 weeks, but they may persist, indicating likelihood of cSCC.
Rare differential diagnoses include amelanotic melanoma, atypical fibroxanthoma and Merkel cell tumour.
Aids to diagnosis
Partial biopsy will generally be unhelpful in differentiating keratoacanthoma from cSCC. Partial biopsy will almost always be reported as SCC because the pathologist requires the architecture of the entire lesion to suggest the possibility of keratoacanthoma.
Practice Point (keratoacanthoma)
PP 4.2.2. Keratoacanthomas should be managed by early excision rather than relying on correct clinical diagnosis and waiting for spontaneous resolution.
Notes on the recommendations
Follow-up of patients after treatment is individually tailored according to patient factors, tumour factors, anatomic site and the perceived adequacy of treatment.
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