ehdog, Many years ago, I experienced something similar. It was biopsied and turned out to be a cyst. Biopsies were different then. Perhaps now an ultra sound (no radiation) would give you some answers and remove unnecessary stress.
Fast forward to 2023 I had pain, in L breast followed by tomosynthesis. The results were negative, I was told to give up caffeine. I did; the pain disappeared. In 2024 annual mammo was negative; six months later in 2025 I found a lump and the next morning called my GYN. I assumed it was a cyst but had it checked out and it turned out to be IDCS. I tell you this not to alarm you but to let you know everyone's experience is different. If you have concerns follow up. Early detection is key. Some lesions are very slow growing and can be assessed periodically, and never need removal, others are more aggressive. The previous comments you have received are correct. Dense breasts can be tricky to diagnose, but it is my understanding from my own research that there is an over diagnoses of breast cancer and most doctors would prefer to err in the side of caution. Talk to your GYN and begin with the least aggressive but best diagnostic method to answer your question and yes, keep watch over the area. Best to you and good luck.