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.
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.
Unfortunately, irregular margins and antiparallel orientation are suspicious features. Make sure you follow through with the recommendations. Good luck!