I'm sorry to hear about your husband's skin cancer. That can certainly be a scary experience, and you're wise to keep a close watch on his skin from now on.
The cracking at the corner of your husband's mouth probably is not cancer, but since he's had a skin cancer once, it would be a good idea to get it checked out by a health care provider. Often, cracking at the corner of the mouth is a symptom of perleche, or angular chelitis. This can be caused by a fungus (which can be treated by your health care provider) or by a Vitamin B deficiency.
However, the symptom you're describing could be caused by many things, including, yes, a cancer. That's why it would be best for your husband to be examined by your primary care provider. He or she can diagnose the problem and treat it accordingly.
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