Not a superficial problem

Recurrent skin cancers may be a bigger problem than they first appear. This superficial basal cell skin cancer had initially been treated with six weeks of imiquimod cream and also had a double freeze with liquid nitrogen, but had recurred. The patient was keen to continue trying topical therapies to avoid surgery and had been referred for photodynamic therapy (PDT). 

PDT works by irradiating with red light tumour cells that have taken up a topical photosensitising chemical. However, the latter only penetrates 2 mm or so into the skin.

Recurrent skin cancers are often deeper, with the tumour trapped in between scar tissue, which neither cream nor light can penetrate adequately to remove the tumour. Recurrent BCCs like this should always be excised. 

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