Association between breast cancer laterality and tumor location, United States, 1994-1998

Cancer Causes Control. 2004 Sep;15(7):637-45. doi: 10.1023/B:CACO.0000036171.44162.5f.


Objective: Cancer is more likely to be diagnosed in the left breast than the right, but the reasons are undetermined. Left-sided predominance has not been evaluated for some demographic groups or by tumor location.

Methods: Laterality was analyzed among 419,935 incident unilateral breast cancers from 26 population-based cancer registries covering 40% of the US population. Logistic regression assessed the independent contribution of race, ethnicity, age, histology, stage, and location to laterality.

Results: Breast cancer was about 5% more likely to be diagnosed in the left breast than the right, a finding that was generally consistent across demographic groups and tumor types. Left-sided predominance was evident among both younger (<45 years) and older women, and among men with either in situ or invasive disease. Among women, tumors in the upper-outer quadrant, where one-third of cancers are located, occurred with equal frequency in the left and right breast, while those in the lower quadrants were about 10% more likely to occur in the left breast.

Conclusion: The observation that the left breast is at greater risk of cancer than the right may not apply to tumors arising in the upper-outer quadrant. The identification of physiologic, pathologic, or immunologic differences between the lower, but not upper, left and right breasts may assist in explaining breast cancer laterality.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Breast Neoplasms / epidemiology*
  • Breast Neoplasms / pathology*
  • Child
  • Female
  • Functional Laterality*
  • Humans
  • Middle Aged
  • Neoplasm Invasiveness
  • Regression Analysis
  • United States / epidemiology