Abstract
BackgroundReduced overall survival has been observed in patients with left-sided versus right-sided breast cancer due to cardiac toxicity after radiotherapy. However, the effect of laterality and primary tumor site on breast cancer-specific mortality (BCSM) remains unclear.Patients and MethodsWe analyzed data from 305,443 women ages 20- to 79-years-old diagnosed with breast cancer between 1990 and 2009. The data were obtained from the population-based Surveillance, Epidemiology, and End Results (SEER) program of the U.S. National Cancer Institute. The survival outcomes with regard to laterality and primary tumor site were compared using univariate and multivariate (Cox proportional hazards regression model) methods.ResultsIn the multivariate analysis, BCSM was affected by the primary tumor site (P<0.0001) but not laterality (P = 0.331). The combined effect was piecewise: using the left upper-outer quadrant as the reference, the BCSM hazard ratio (HR) was not significant in the right upper quadrant (P = 0.755) and the right central portion (P = 0.329). The BCSM HR was slightly increased in the left central portion as well as the left and right lower-outer quadrants (HRs from 1.136 to 1.145; P<0.0001). The BCSM HR was significantly increased in the upper-inner and lower-inner quadrants (HRs from 1.242 to 1.372; P<0.0001) on both sides. Laterality only impacted BCSM in patients with breast cancer located in the central portion (HR, 1.100; P = 0.013, using the right side as the reference).ConclusionPatients with tumors in the upper-outer quadrant of both sides and the right central portion have a better prognosis than patients with tumors at other locations. Laterality is not regarded as a prognostic factor in breast cancer.
Highlights
In-depth studies in the field of breast cancer preferably describe breast cancer using various characteristics, such as age, histologic grade, local tumor size, regional lymph node involvement, presence of lymphovascular invasion, hormone receptors and HER2/neu status, given the prognostic value of these factors in breast cancer survival [1,2,3]
The breast cancer-specific mortality (BCSM) hazard ratio (HR) was slightly increased in the left central portion as well as the left and right lower-outer quadrants (HRs from 1.136 to 1.145; P,0.0001)
Patients with tumors in the upper-outer quadrant of both sides and the right central portion have a better prognosis than patients with tumors at other locations
Summary
In-depth studies in the field of breast cancer preferably describe breast cancer using various characteristics, such as age, histologic grade, local tumor size, regional lymph node involvement, presence of lymphovascular invasion, hormone receptors and HER2/neu status, given the prognostic value of these factors in breast cancer survival [1,2,3]. The presence of IMC metastases depends on tumor location in the breast; a higher prevalence of IMC metastases in tumors of the inner quadrants has been noted, especially in the lower-inner quadrant [6] In this regard, the primary tumor site cannot be neglected in a systemic evaluation of breast cancer. Since the last decade of the twentieth century, an increased risk of mortality due to ischemic heart disease has been observed in women with breast cancer treated with radiotherapy Among these patients, an excess of cardiac deaths was noted in leftsided breast cancer compared with right-sided breast cancer [7,8]. Given the improvement of radiotherapy techniques and protective measures, radiation-related mortality has substantially decreased in recent years [9] Despite these studies, the influence of laterality on breast cancer-specific mortality (BCSM) remains unknown. The effect of laterality and primary tumor site on breast cancer-specific mortality (BCSM) remains unclear
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