Dear Nancy, You are doing an appropriate thing by seeking a second opinion from a breast specialist. See what the recommendation from the breast surgeon is. They will be looking at the actual films and test results, and doing a physical exam and make their recommendations based on the findings.
the decision to biopsy depends on lots of things, including your own level of concern. If that's what will give you the most reassurance, that's what you should do. But the surgeon may be able to explain things and reassure you also. Lymph nodes can enlarge for many reason, most commonly some infection or inflammation that you might not even have noticed at the time. Some mammogram shadows are pretty definite that it's a lymph node and harmless, especially if fat is seen in the center of it.