Breastfeeding issues: help!

My sister went in for an ultrasound today, and they found a cyst in her breast about 2 cm in size. They didn't send her for a mammogram, so she’s planning to head over to a private clinic for a follow-up exam. She's only 23.
Basically, I’m just trying to figure out if this is actually dangerous? I've heard rumors that having even a single cyst can be a bad sign or indicate something malignant.
Does anyone here have any actual experience with this or some insight to share? Please, let me know what you know...😕

Thanks!

Just a quick follow-up on this: my ultrasound report actually mentions fibrocystic changes.

Lisa Kelly53 said:update: the ultrasound report says fibrocystic

Look, fibrocystic breasts—or fibrocystic breast changes—are super common among women. It’s officially called fibrocystic breast dysplasia... and before you panic, it's totally non-cancerous.

Honestly, you can find pretty much everything on this if you just Google "fibrocystic breasts."