When we think about breasts, we think about cleavage, mammary folds, and cup sizes. And many people think that's the extent or limit of the breast's tissues—what's in the cup (or spilling out of it).

In fact, however, breast tissue extends much farther than this—up to the clavicle bone, above the breast mound, around and underneath your armpit, and down to the band of your bra. Yep, it's much more extensive than you might have thought.

All of which means that when a mammo tech is doing a mammogram, she is going to be tugging on you so she can get as much breast tissue onto that x-ray film as possible: not just the breast mound but more, especially the tissue that rests on your chest muscles. (Actually, if the tech has done a good job, we should be able to see your chest muscles on the mammogram x-ray.)

And likewise when you're doing a breast self exam: Don't concentrate only on the breast mound. Remember that 70 percent of breast cancers are found in the upper outer quadrant of the breast—the area closest to your armpit. It all deserves your careful, thorough attention. So, check it all out.