Biopsy that wasn’t really needed?

Radiologists use the BIRADs system to assess imaging and determine next steps.

As you can see from the chart below, "tissue diagnosis", i.e. a biopsy, is recommended for any imaging that a Radiologist assesses to have a 2% or greater chance of being cancer. That's a BIRADs4. The thing to understand with the Radiologist's assessment is that lots of different conditions look the same on imaging. Mammograms and ultrasounds and even MRIs are not precise and cannot provide a diagnosis. All they can do is show that something is there. From the appearance, the 'something' might look relatively benign or it might look quite suspicious, but the only way to know for sure is with a biopsy.

That said, there are certain lesions - cysts, fibroadenomas, many types of calcifications - that if they meet several benign critieria, can be quite safely identified as being benign. Those are usually assigned a BIRADs3, with a short term follow-up to confirm stability (cancer will grow and change and not be stable). A few, such as simple cysts (round or oval, thin even walls, fully fluid filled with no solid particles) or some types of calcifications (macrocalcs, large, coarse, diffuse/randomly scattered) are so clearly benign that they get a BIRADs2.

In your case, you had a small nodule. My guess, since it turned out to be fatty breast tissue, is that there was no blood supply, which would have leaned the assessment towards benign. But the mass would have appeared on imaging to be solid, and being a blob of fat, the shape and edges might not have been completely clean and well defined. That would warrant a biopsy because while the overall impression of the mass might give the appearance of being benign, there certainly could be more than a 2% chance that it might be cancer.

And yeah, I've had 7 breast biopsies over the years, and most ended up benign. One turned out to be a fatty deposit. I've also had several BIRADs3 assessments for complicated cysts (basically simple cysts but with a solid debris). None of those ever turned out to be anything, and none required a biopsy after follow-up screening. I trust that my Radiologist knows her stuff and is looking out for my best interest when assigning a BIRADs number.

I can't comment on your side note except to say that perhaps you should ask about that, or read the report to see if any reference is made to the location of the nodule as compared to the imaging.

Glad that the info was helpful!