Us didn't show the mass. i can definitely feel a 4 cm mass deep in soft tissue. could it have been missed? of this was a cancer would it show?

It depends: Where is this mass that you are feeling? Ultrasound is a good test but it can sometimes miss masses. So if you feel something,, ask your doctor to check it. He/She may order a CT scan which is more reliable test than an ultrasound.. Between physical exam and CT can we can generally get a good idea if there is any tumor present. If this lump is in the breast a mammogram is another good test to chec