How do i know if breast lumps are benign or malignant?

Need 2 C Ur Doctor: It is difficult if not impossible to differentiate a benign breast tumor from a malignant one by exam alone. An ultrasound +/- mammogram may be very helpful; ultimately, a (needle) biopsy under local anesthesia in an office setting is the most definitive diagnostic method. I advise you to see your doctor for the appropriate direction.

See a doctor: By yourself, you cannot tell if a breast lump is benign or not. Is it new or changing? Painful or not? You really must see a doctor for a physical examination & likely mammogram and/or breast ultrasound. Do not try to guess yourself without a doctor's exam.