How can you tell if a breast lump is serious?

Go to your doctor: The best way to know whether a breast lump is serious is to have your doctor evaluate it and order the appropriate studies.

Only way to : Tell for sure whether or not it is cancer is with biopsy. But mammogram and physical exam will give a good indication on which lumps require biopsy. Get to a doctor.

Don't know yet: At your age, the odds are any lump is benign. However, by the time you feel a lump, it could already be cancer. Please see your doctor for a complete history and physical, and if appropriate, additional imaging with ultrasound and perhaps mammography. Given your age, us first may be useful, since if the lump is really a simple cyst, a mammogram may not be necessary.