A female pt. present with a hard. mobile lump in her rt. breast. Which investigation would be most helpful in making the diagnosis -

An open biopsy is the most definitive investigation. CSDT writes - "The most reliable diagnostic test for breast cancer is open excisional biopsy. When the sample is properly taken by the surgeon and examined by the pathologist, such a test should give no false-negative and no false-positive results." " Large-needle (core needle biopsy) is an accepted diagnostic technique n which a core of tissue is removed with a large cutting needle. As in the case of any needle biopsy, the main problem is sampling error due to improper positioning of the needle, giving rise to a false negative test result."