In lobular carcinoma because: High chance to predispose to invasive carcinoma. 35% of lobular carcinoma in situ may devolop invasive lobular carcinoma either in the same or contralateral breast, 65% may devolop invasive ductal carcinoma. It is multifocal, bilateral(50%). So biopsy from opposite breast should be taken. Reference: SRB's Manual of Surgery, 6th Edition, page no = 526.