Severe Atypia. Is It cancer?

I had a biopsy of a mole on my back and results came back as severely atypical. I am scheduled to have it excised next week. Will they put it under the microscope again to determine if it is indeed cancerous? Or do they just excise it now since it's very precancerous? How do they know if they remove all the "cancerous" cells if they don't even know with 100% certainty if it's cancerous? Will this excision (which will require stitches) be the final step for this mole?

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