Left and right sided breast cancer.

Area of Science:

• Oncology
• Epidemiology

Background:

• Unilateral breast cancer incidence is notably higher in the left breast compared to the right.
• Previous research indicates a left-sided predisposition for primary breast cancer.

Purpose of the Study:

• To investigate the laterality of breast cancer in the Icelandic population.
• To examine the risk of contralateral breast cancer in women with a history of unilateral breast cancer.
• To assess the impact of family history on contralateral breast cancer development.

Main Methods:

• Analysis of 2139 female breast cancer cases diagnosed between 1948 and 1987 from the Icelandic Cancer Registry.
• Categorization of cases into unilateral and bilateral primary breast cancer.
• Evaluation of contralateral breast cancer risk based on initial diagnosis side and family history.

Main Results:

• A 13% excess of unilateral breast cancer cases occurred in the left breast (1069 left vs. 942 right).
• Women with a history of unilateral breast cancer maintained an increased risk for left-sided contralateral breast cancer.
• A 2.54-fold increased risk of contralateral breast cancer was observed in patients with a first-degree affected relative.

Conclusions:

• The left breast exhibits a higher susceptibility to developing primary breast cancer.
• A history of unilateral breast cancer does not negate the increased risk for the contralateral left breast.
• Family history is a significant risk factor for developing contralateral breast cancer, particularly in right-sided initial diagnoses.