All breast lumps should be thoroughly checked out. This is often done in steps starting with the least invasive. If you find a lump, go to an oncology surgeon. Your gynecologist can refer you or they can be found at most major hospitals. Hospitals now often have Breast Health Centers too.
Oncology surgeons are the ones that diagnose the most breast cancers.
The surgeon will do a breast exam, probably order a mammogram and maybe an ultrasound. Many hospitals do these tests within days of your visit. A needle biopsy may be done during the visit to the surgeon. Needle biopsy are screens only, if they show cancer you have it, if they don't you still may have it. During a needle biopsy, the needle is passed in and out of the lump.