Mohs: What is Skin Cancer?

 Skin cancer is by far the most common malignant tumour in humans. The most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma and melanoma. Both basal cell carcinoma and squamous cell carcinoma begin as a single point in the upper layers of the skin and slowly enlarge, both along the surface and downward. These extensions cannot always be seen directly. The tumour often extends far beyond what is visible on the surface of the skin. Basal cell carcinoma metastasis (spread) is extremely rare, and usually only occurs in the setting of long-standing, large  tumours. Squamous cell carcinoma is slightly more dangerous and patients must be observed for any spread of the tumour. Such spread is still infrequent. 

FIGURE 1

– depicts skin cancer where a vertical cut has been taken, which would be interpreted as clearance of the tumour (a), but one can see that if the cut had been made in another site where the tumour did extend to the margin (b), the result would have been a positive. Hence because of the random intermittent section of tissue, inevitably tumour can be present at excision margins without detection.