Small Breast Lump Disappearance: What Could It Be?

Question
I'm 44 and at my clinical exam my dr. found a small, rubbery lump that was close to the surface near the nipple.  I had my annual physical exam 5 days later and neither this dr. nor I could not feel anything but she suggested that since the initial exam was 3 days into my cycle that it could have been a cyst that just resolved.  I went for my diagnostic mammogram and 10 days later got a call that the radiologist wanted an ultrasound.  The only thing they told me was that there was some density but no suspicious microcalcifications. When I asked if they could see a lump, she said there was no notation of that finding.  Also - I have no family history of cancer.

I have small breasts that are fairly fibrocystic.  Is it more difficult to get clear pictures from a mammogram in this situation?  What could the density issue involve?  Is it routine to request an ultrasound in this situation?

Finally, I have done several IVF cycles this past year with injectibles (and had just come off one cycle when I had my exam).  Do these types of medications have any effect on breast changes?
Thanks so much.  I appreciate your time.

Answer
Yes it was probably a cyst. If your breasts are fibrocystic they will also be dense and that will impair the use of mammography. What has been found is rather typical in that situation. This makes ultrasound breast scans AND EVEN MORE IMPORTANT MRI breast scans necessary in your case as in all other such cases! Your fibrocystic condition is hormone dependent so your efforts may have influenced your condition. I'm somewhat surprised that your drs. have not discussed this with you!