How does a doctor diagnose breast cancer?

Biopsy: The only way to DX with certainty is to look at tissue under the microscope. Most women are diagnosed with breast cancer after an abnormality is found on a routine mammogram or if a lump is palpated (by patient or doctor). In each scenario, (non-surgical) needle biopsy will lead to the diagnosis.

Exam and imaging: Breast examination, mammography and ultrasound. Sometimes mri. Anything suspicious on any of these examinations lead to biopsy - usually with a core needle.

With a breast: biopsy. Lesions requiring biopsy can be identified on physical examination and/or mammography and other imaging studies.