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The description you gave is pretty vague.
Are your breasts nodular in feel? This is normal but some breasts may feel nodular and when examined down to the line of the armpit, then a margin where breast tissue ends may be an edge. These are all within normal breast examinations however.
Other situations may involve tumor infiltrating the tail of the breast near the armpit - this would be clearly "mass" so this doesn't sound like a plausible explanation.
Best wait for results, and on your part familiarize yourself with your breasts. It may be best to locate the edge with the help of the doctor so you could also monitor it.
Stay positive.