Oh gosh, I hate to hear that you are called back with some findings during a routine mammogram. When you say lumpy breasts, you mean dense breast tissue. This is not uncommon and many women develop this more and more as they get older. I have dense breast tissue myself. That density may be 'more' likely to hide breast cancer and the odds of breast cancer go up when someone has dense breasts but this is not cancer in itself. Here's info on breast density. https://www.cdc.gov/cancer/breast/basic_info/dense-breasts.htm Now, it does say that you have a higher risk of breast cancer with dense breasts. This means, don't miss your mammograms.
Okay, so now to your findings. I am sure that is scary. Normally they do another mammogram. Yes, lobulated masses typically are benign. Did they see anything else like calcifications? That it was partially obscured, that's not unusual with dense breasts. Again, they normally always take a second look with either a 3D mammogram or ultrasound.
I had suspicious calcifications and was given a Bi Rad of 5. The Bi Rad scale is what the radiologist who reads the images gives to the findings if they are abnormal. The scale is 0 to 6. 6 is definite cancer. Needless to say, my Bi Rad of 5 was terrifying. I went straight to a breast surgeon and a biopsy was performed. (I did NOT have cancer, by the way). So, please know that they do act fairly quickly typically if something is suspected cancer. Yours likely is not. But I do understand that you are scared and nervous. Have you had a chance to speak to your doctor yet?
On mammography, the margin of a lesion can be described as circumscribed, obscured, microlobulated, indistinct, or spiculated (listed from least suspicious to most suspicious). Given your age and history of lumpy breasts, the most probable diagnoses are benign cysts and/or fibroadenomas. At this point, I would not be overly concerned. Many women get callbacks, and most of those callbacks turn out to be benign. Just take things one step at a time and be sure to return for your follow-up appointment, which will likely include at least a breast ultrasound to further characterize the masses. Good luck!