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Author: Samuel Der Sarkissian, General Practitioner, Shellharbour Medical Centre, NSW, Australia. DermNet NZ Editor in Chief: Adjunct A/Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. March 2020.
A keratinocyte cancer is a malignant neoplasm formed from the epidermal cells that produce keratin (keratinocytes). Keratinocyte cancers are classified as either squamous cell carcinomas (SCC) and basal cell carcinomas (BCC).
Keratinocyte cancers are considered low risk or high risk, depending on patient factors such as age, immune suppression status, histological subtype, and the site of the tumour on the body.
A surgical margin is a clinical measurement made just before a lesion is excised. The surgeon uses their naked eye or magnification (eg, a dermatoscope) to find the edge of the tumour, then measures the desired amount of normal skin to remove on either side of the tumour. A surgical marking pen is used to plan the excision site.
As a general guide, adequate surgical margins are 3–4 mm for a BCC and at least 4 mm for a low-risk SCC. There are no published guidelines for a high-risk SCC.
A histological margin is measured by a pathologist. It describes the amount of normal tissue bordering a tumour specimen.
Histological margins may be adequate, narrow, or inadequate.
An adequate histological margin is the acceptable distance of tumour cells from the histological margin, according to expert consensus and published research.
The desirable margin depends on the type of tumour and the technique used to remove it. Clinicopathological correlation and additional sections may be useful, particularly when clinical margins have been difficult to assess or compromised by the anatomical location of the tumour (eg, mid-facial lesions).
Adequate histological margins are generally:
Margins greater than 1 mm are considered adequate for high and low-risk SCC .
Margins less than 1 mm mandate careful monitoring or further treatment .
The high-risk features of each type of keratinocyte cancer are as follows.
High-risk BCC can possess the following features:
High-risk basal cell carcinoma
High-risk SCC can possess the following features:
High-risk squamous cell carcinoma
Perineural invasion may be seen on histology in up to 5% of keratinocyte cancers. It poses a high-risk for local recurrence, and in SCC, for metastasis .
Tumours with perineural invasion should be referred to a specialist. Management may include:
If the histological margins are involved or inadequate, most low-risk BCCs should undergo re-excision to ensure adequate margins. In select cases, radiotherapy may be a reasonable alternative. Persistent superficial BCC may occasionally be treated topically (eg, imiquimod cream).
Inadequately excised high-risk lesions should be referred to a specialist, depending on the clinician’s skill and tumour factors. To reduce unnecessary removal of healthy tissue, Mohs micrographic surgery may be considered, especially for lesions in high-risk areas.
Histological margins of less than 1 mm should lead to re-excision of an SCC. Consider getting a referral for high-risk SCCs, especially on the head and neck.
Recurrence of a keratinocyte cancer depends on the type and risk category of the lesion, the type of treatment, the histological margins, and the clinician’s expertise.
For low-risk BCCs treated by surgical excision:
Recurrent basal cell carcinoma
BCCs rarely metastasise but can cause local tissue destruction. Recurrent BCCs usually require more aggressive treatment resulting in greater tissue loss and surgical complications.
Development of local recurrence of SCC is associated with further local recurrence in about 25% of lesions and subsequent metastasis to regional nodes in up to 30%. About a third of patients who develop regional metastasis will die of SCC .
Recurrent BCC is treated by resection of the scar, the recurrent tumour and a 3–4 mm margin of surrounding skin [10,11]. Specialist referral should be considered, especially if the tumour edges are hard to detect. Mohs surgery may be indicated.
Specialist referral is recommended for recurrent SCC due to the risk of developing further recurrence and metastasis.
Follow-up requires inspection of the treated area using dermoscopy and palpation of adjacent structures .
An annual skin check is recommended for all patients with a history of skin cancer.
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