What Causes Cyst In Breast With History Of Thyroid Cancer?

i had thyroid cancer 14 years ago recently they found a 5 x3 mm hypoechoic nodule in my breast and a cyst nest to it. they are doing a biopsy tomorrow. do they usually do biopsies for this or do they take a wait and see approach. are they doing the biopsy because of my previouscancer.