CC is a struct including the field PixelIdxList. If you define the area as number of pixels, you just need the number of elements of each cell:
elemsize=cellfun(@numel,CC.PixelIdxList);
To remove the small ones (I define "small" as "less than 100 pixels"):
BW2=BW;
BW2(vertcat((CC.PixelIdxList{cellfun(@numel,CC.PixelIdxList)<100})))=0;
You can of course do this without copying BW (just ignore the first line and use BW instead of BW2 in the second line).
Edit: If you also want to remove these from CC:
CC.PixelIdxList(cellfun(@numel,CC.PixelIdxList)<100)=[];
CC.NumObjects=numel(CC.PixelIdxList);
