Metastatic Potential of SCCs
Anatomical site has a major influence over the metastatic potential of the tumour. Other influences increasing metastatic potential include; the size, tumour thickness, level of invasion, rate of growth, aetiology, degree of histological differentiation and host immunosuppression.
The list below is ranked from lowest to highest risk of metastasis (British Association of Dermatologists)(10)
- SCC arising at sun-exposed sites excluding lip and ear
- SCC of the lip
- SCC of the ear
- Tumours arising in non sun-exposed sites (e.g. perineum, sacrum, sole of foot)
- SCC arising in areas of radiation or thermal injury, chronic draining sinuses, chronic ulcers, chronic inflammation or Bowen’s disease.
The size of the SCC has a bearing on metastasis potential also; Tumours >2 cm in diameter are twice as likely to recur locally and three times as likely to metastasize compared with smaller SCCs. Tumours greater than 4 mm in depth (excluding surface layers of keratin) or extending into or beyond the subcutaneous tissue are more likely to recur and metastasize compared with thinner SCCs. SCCs less than 4mm in depth confined to the upper half of the dermis are much less likely to reoccur or metastasise. SCCs < 2mm thickness rarely metastasise.
Host immunosuppression is associated with a poorer prognosis; Patients who are immunosuppressed generally have a poorer prognosis. These patients tend to have increased locally invasive SCCs which are more likely to have metastasised.
Treatment modality can affect recurrence; The risk of recurrence is dependent on the previous treatment modality. Moh’s micrographic surgery is associated with the least recurrence.
Management
All suspected SCCs should be referred as an USC.
There are three main factors, which all specialities (Dermatology and Plastics) agree influence treatment for SCC of the skin and the vermilion border of the lip (excluding SCCs which occur on the penis, vulva, anus, SCC in- situ, SCC arising from mucous membranes and keratoacanthoma);
- The need for complete removal or treatment of the primary tumour
- The possible presence of local metastases
- The tendency of metastases to spread by lymphatics to regional lymph nodes
Guidelines for treatment of SCC should be interpreted with the following considerations in mind;
- There is widely varying malignant behaviour of tumours which fall within the histological diagnostic category of primary cutaneous SCC.
- There is a lack of randomised controlled trials (RCTs) for the treatment of primary cutaneous SCC.
- Plastic and maxillofacial surgeons may encounter predominantly high-risk, aggressive tumours, whereas dermatologists may deal predominantly with smaller and less aggressive lesions leading to variation in management approaches.
For treatment of superficial SCC Surgical excision is the treatment of choice. For clinically well-defined, low risk tumours less than 2 cm in diameter, surgical excision with a minimum 4-mm margin around the tumour border is appropriate. Less than this could leave residual tumour.
SCCs more than 2 cm in diameter moderately, poorly or undifferentiated, extending into the subcutaneous tissue or those on the ear, lip, scalp, eyelids or nose should be removed with a wider margin such as 6mm or more. The tissue should always be examined for histology or with Mohs micrographic surgery.
Should an SCC metastasise this is usually via local lymph nodes and clinically enlarged nodes should be examined histologically (for example by fine needle aspiration or excisional biopsy). Any positive lymph nodes are managed by regional node dissection.
Ultimately from a primary care point of view the management is an USC referral, and for secondary care to continue ongoing management. With a need for ongoing research and consensus on overall management. (10)