Breast masses are a common clinical finding, and may be palpable or nonpalpable, benign or malignant. The majority of palpable breast masses are benign, but 10% of women who present with this finding will have a diagnosis of cancer.  Approximately 4% of breast cancers will present with a palpable mass and no mammographic or ultrasonographic evidence of disease. 
A delayed or missed breast cancer diagnosis can severely affect patient outcome.
Evaluation of a breast mass is guided by findings on history, physical exam, imaging, and biopsy. A triple test of clinical breast exam, imaging (e.g., mammography and ultrasonography), and needle biopsy can lead to a definitive diagnosis in nearly all cases.   
Fellow in Breast Surgery
Breast Surgery Unit
The Royal Marsden Hospital NHS Foundation Trust
M-KT declares that he has no competing interests.
Dr Marios-Konstantinos Tasoulis would like to gratefully acknowledge Professor Anees Chagpar and Dr Matthew Bower, previous contributors to this topic. AC and MB declare that they have no competing interests.
Director of Surgical Oncology
Department of Surgery
University of Oklahoma
G. Rainey Williams Chair in Surgical Breast Oncology
OU Breast Institute
WD declares that he has no competing interests.
Hospital Universitario Ramon Gonzalez Valencia
JE declares that he has no competing interests.
Consultant Medical Oncologist/Senior Lecturer
Department of Medical Oncology
Imperial College/Imperial Healthcare NHS Trust
Charing Cross Hospital
JS declares that he has no competing interests.
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