Girls, breast cancer?

Okay, im 15, athletic, and i noticed that i have a lump in my left boob... I dont know if it should be a concern. There is like one knot with 3 little ones branching off.. I dont want to say anything to my family and have them scared, but i kinda am.. My grandma had breast cancer. She passed away from ALS a couple of months after the fight with cancer.. So im afraid of genetics too... Please any help is greatly appreciated!!
Girls, breast cancer?
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