<s>[INST] I had a mammogram and a breast sonogram, both revealed a small (5 mm) mass under the nipple, it has not been diagnosed as cancer, it is thought to be benign, however a biopsy was recommended to be sure. I don t think it is necessary because I had this before and was told it was a cyst (benign) that is very common, they come and go. I have never had a biopsy before. Your thoughts? [/INST] HiSince your mammogram and breast sonogram revealed 5 mm mass i would advice you to go for the biopsy test just to confirm that it is not cancerous.It is a simple procedure where a thin needle is inserted into the mass which removes a sample of cells or fluid to look under the microscope.RegardsDR DE </s>