Abstract Purpose:This study was performed to analyze the risk of second non-breast primary cancers (2nd_PrimaryCa) among Korean women who had received curative treatment for breast cancer. Methods:By using data from the Korean National Health Insurance Service Database between 2002 and 2017, we identified 399,621 women with invasive breast cancer. To analyze the long-term risk of 2nd_PrimaryCa, we included 52,506 women who underwent curative surgery between 2003 and 2008, and no history of cancers before the date of breast cancer surgery. The cumulative incidence of 2nd_PrimaryCa was estimated using the Kaplan-Meier analysis. Cox regression analysis was used to analyze the association between 2nd_PrimaryCa occurrence and factors including age, income level, receipt of systemic treatment or radiotherapy, family history of cancers, alcohol intake, and BRCA gene mutations.Results:A total of 3,084 (5.87%) patients developed 2nd_PrimaryCa. The 10-year incidence of 2nd_PrimaryCa was 5.78% (range, 5.56 – 6.00%). The median time to 2nd_PrimaryCa was 7.61 years (range, 6.22 – 9.31 years). Types of organs involved by 2nd_PrimaryCa were as followings: thyroid (18.84%), gynecological organs (12.78%), hepatobiliary structures (12.48%), thorax (11.25%), lower gastrointestinal (GI) tract (9.63%), upper GI tract (9.18%), skin (4.22%), lymphoma or leukemia (4.09%), brain (3.15%), head and neck (2.56%), and others (11.84%). The risk of 2nd_PrimaryCa was significantly associated with ≥ 60 years of age (hazard ratio (HR) = 2.15, 95% confidence interval (CI) = 1.60 – 2.90, p < 0.01), Medical Aid recipients (HR = 8.79, 95% CI = 6.73 – 10.85, p < 0.01), and receipt of chemotherapy and endocrine therapy (HR = 1.27, 95% CI = 1.12 – 1.43, p < 0.01). Radiotherapy was related to lower incidence of 2nd_PrimaryCa (HR = 0.87, 95% CI = 0.81 – 0.94, p < 0.01). Alcohol intake, family history of cancer, or carrying BRCA gene mutations was not related to the risk of 2nd_PrimaryCa. Among the patients with 2nd_PrimaryCa, the 5-year overall survival (OS) rate was 67.28% after the diagnosis of 2nd_PrimaryCa. Age of ≥ 60 years (HR = 1.67, 95% CI = 1.01 – 2.78, p = 0.04) and receiving chemotherapy and endocrine therapy (HR = 1.88, 95% CI = 1.43 – 2.46, p < 0.01) were significantly related to inferior OS. Conclusions:The risk of 2nd_PrimaryCa was associated with personal and treatment factors in Korean patients with breast cancer. These factors are needed to be considered in the surveillance of breast cancer survivors. Citation Format: Haeyoung Kim, Su SSan Kim, Ji Sung Lee, Jae Sun Yoon, Hyuk Jai Shin, Jeong Eon Lee, Sei Kyung Lee, Il Yong Chung, So-Youn Jung, Young Jin Choi, Korean Breast Cancer Society. Risk of second primary cancers after curative treatment of breast cancer: A Korean nationwide population-based study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-25.

This article provides an annual update of Korean breast cancer statistics, including the incidence, tumor stage, type of surgical treatment, and mortality. The data was collected from the Korean Breast Cancer Society registry system and Korean Central Cancer Registry. In 2019, 29,729 women were newly diagnosed with breast cancer. Breast cancer has continued to increase in incidence since 2002 and been the most common cancer in Korean women since 2019. Of the newly diagnosed cases in 2019, 24,820 (83.5%) were of invasive carcinomas, and 4,909 (16.5%) were of carcinoma <i>in situ</i>. The median age of women with breast cancer was 52.8 years, and breast cancer was most commonly diagnosed in the age group of 40-49 years. The number of patients who have undergone breast conserving surgery has continued to increase since 2016, with 68.6% of patients undergoing breast conserving surgery in 2019. The incidence of early-stage breast cancer continues to increase, with stage 0 or I breast cancer accounting for 61.6% of cases. The most common subtype of breast cancer is the hormone receptor-positive human epidermal growth factor receptor 2-negative subtype (63.1%). The 5-year relative survival rate of patients with breast cancer from 2015 to 2019 was 93.6%, with an increase of 14.3% compared to that from 1993 to 1995. This report improves our understanding of breast cancer characteristics in South Korea.