How would you treat this upper chest lesion?

This is an engaging case from Dr Tim Aung. A 55-year-old female presents with 1-2 years' history of slow growth of an asymptomatic, non-tender lesion on the upper chest. Please review the images.

What is your impression, what is the differential diagnosis, and (if you would biopsy) what technique would you use?

Update

These are the results from the pathology report. What do you think now? How would you treat further?