Abstract P1-05-29: Breast cancer laterality: Is age a factor?

Abstract BACKGROUND: Studies have consistently demonstrated that breast cancers arise in the left breast more often than the right breast, but no factors have been able to account for this. Some studies have shown age younger than 45 years and late age at menarche to be associated with somewhat higher incidence of cancer in the right breast. However, most of these studies were conducted in the 1990s. We sought to determine if demographic factors, pathologic findings, or treatment impact laterality. METHODS: We performed a single-institution IRB-approved retrospective chart review of US female breast cancer patients diagnosed with DCIS (stage 0) or stages I-III breast cancer from 1997 to April 2020. Clinicopathologic characteristics, demographic, and treatment information were collected. Statistical analyses evaluated differences in laterality. Association between laterality and continuous variables was determined using Kruskal-Wallis test. Association of laterality and categorical variables was determined using Chi-square test or Fisher exact test if applicable. RESULTS: 5328 female patients with 5474 breast cancers were evaluated with a median age of 60 years old. Majority of tumors were stage T1(2542, 54.4%) and 75% were IDC. Overall left-sided cancer showed a predominance (2797, 51.1%). Breast cancer laterality was not significantly associated with grade, receptor status, tumor size, pathologic type, or recurrent tumors. Laterality was evaluated regarding age, based on age less than 61 years old versus greater than or equal to age 61. Laterality was significantly associated with age overall with an increase in left-sided breast cancers (2797 vs 2677, p=0.029). Left-sided breast cancer was significantly increased in women greater than or equal to age 61, 1456 (53%) vs right-sided 1290 (47%). Whereas, right-sided breast cancer was significantly associated with age less than 61, (1387, 50.8% vs left 1341, 49.2%, p=0.004). CONCLUSION: Our analysis confirms prior studies that overall left-sided breast cancer is more common in women. However, there are age differences with left-sided breast cancers more prevalent in older age women greater than or equal to age 61. On the other hand, right-sided breast cancer was seen more often in women under the age of 61. Further studies are needed to better ascertain why the overall laterality of breast cancer occurs more frequently in the left breast, but also to determine an explanation for the laterality age differences. Anatomical factors such as blood supply, breast size, inherited genetic mutations, tumor genomics, lactation history and others are possible factors that need to be further explored. Studies are ongoing. This information will be potentially helpful in allocating diagnostic and therapeutic resources for breast cancer patients. Citation Format: Kelly Elleson, Gerald H. Sokol, Weihong Sun, Junmin Whiting, Marie C. Lee, Brian J. Czerniecki, Loretta Loftus. Breast cancer laterality: Is age a factor? [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-05-29.