How to tell if it's a breast cancer or other lump?

Breast mass: Other than a biopsy of the lump there is no guaranteed way of telling is something is a cancer or not. Mammogram, ultrasound or breast MRI may indicate the lump has a higher risk of cancer because of shape, calcifications within the lump or reaction around it but none of those are a sure way to diagnose it. Biopsy is still the only way to really diagnose it.

See your doctor: It is very difficult to distinguish a benign breast lump from a cancer for patient and doctor. Depending upon age and physical examination findings, we will often get a mammogram and ultrasound to help evaluate a breast lump, sometimes culminating in a (nonsurgical) needle-biopsy--ultimately, the only way to be 100% certain is to look at the tissue under the microscope.

Biopsy: It often requires a biopsy, needle or open, or fine needle aspirate to differentiate a benign lump from cancer. Please consult your doctor.

Eval by breast surg: If there's a new lump that's drawing attention/concern, seek immediate medical attention and referral to a breast surgeon. Beyond clinical impression, imaging will often suggest what the lesion is but the most definitive diagnosis usually comes via a needle (i.E aspiration or core biopsy).

Biopsy: The only way to know for sure if a breast lump is cancer or not is with a biopsy - a procedure in which a small amount of the lump is removed and then examined by a pathologist under the microscope. Mammogram, ultrasound and MRI can give a good idea if a lump is cancer or not, and depending on the results of imaging studies, biopsy may not be necessary.

Pathologist: The lump should be biopsied or removed and the tissue examined by a pathologist to arrive at the correct diagnosis.