Unfortunately, irregular margins and antiparallel orientation are suspicious features. Make sure you follow through with the recommendations. Good luck!
Arghh. That's always scary. Do you think they misdiagnosed it as a cyst early on? I had a cyst in my breast that was aspirated. In the other breast I had calcifications that needed biopsy, birad 5 (scared the total poop out of me). What is your next step to learn more? Oh, and by the way, birad 5 and no cancer. So, try not to worry until you have to.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4644748/ - according to this, "irregular hypoechoic mass" can mean quite a few different things, and definitely not always cancer. They found that some were foreign matter, fat tissue, scar tissue, etc.
I also found this - https://www.breastcancer.org/symptoms/benign/cysts - "About 25% of all breast masses turn out to be cysts."
So there's still a decent possibility that this is still a cyst, or it's something else entirely.
I couldn't find much about a cyst turning into a mass.
I'm sorry you have to wait. The waiting is the worst part of medical treatment, I think.
Let us know what happens.