Mammogram showed grape size white area. had view redone because breast tissue wasn't compressed. 2nd test the "grape" not there. why? concerned?

Try not to worry : This is common and a big source of confusion and concern for patients. When taking the picture of the breast, tissue sometimes randomly overlaps and will appear denser (white) than it should. This happens roughly 10% of the time. The only way to know this isn't cancer is to take another picture. If it disappears (it usually does) then you know it's tissue overlap, not cancer. I hope this helps!

Yes, it is possible: Initial mammogram may have not had enough compression in that spot, or the overlapping structures may have caused a "summation shadow". The spot views provide focal compression over the area of concern and spread out the tissues more, to make sure there is nothing of concern in that area.

A mammogram: is a 2D representation of a 3D structure. Occasionally some normal breast tissue will overlap with tissue in front of it,or behind it, and create the illusion of an abnormality on the mammo picture. The extra views spread the tissue out in order to prove that it is normal. A true mass will never spread out.