对于乳腺癌患者而言，对侧乳腺癌（CBC）是最常见的原发性癌症。尽管许多研究已报告了CBC发生后的生存情况，但结果并不一致。为了调查CBC的发展是否与乳腺癌患者的生存相关，本研究在韩国阿山医学中心进行了队列研究，涵盖了1999年至2013年期间被诊断为原发性单侧、非转移性、0～III期乳腺癌的患者，并对其进行了直到2018年结果的随访。中位（IQR）随访时间为107（75-143）个月。根据随访期间是否发生CBC将患者分为CBC组和非CBC组。数据分析时间为2021年11月至2023年3月。本研究的研究目的是探讨CBC的发展是否与乳腺癌患者的生存相关。对整个研究人群进行CBC和非CBC组的存活率比较，使用时间相关的Cox比例危险模型，并进行不同CBC发展时间间隔和原发性乳腺癌亚型的亚组分析。研究对象为16,251例乳腺癌患者（均为亚洲人，具体为韩国人；平均年龄[SD]为48.61 [10.06]岁），其中418例患者发展了CBC。在CBC组和非CBC组之间的总体生存率之间没有显著差异（风险比1.166，95% CI为0.820-1.657）。在原发性乳腺癌手术后1.5年内发展CBC的患者在研究期间的总体死亡风险更高（风险比2.014，95% CI为1.044-3.886），而在1.5年后发展CBC的患者与非CBC组相比，生存率没有显著差异。激素受体（HR）阳性和人表皮生长因子受体2（ERBB2，以前为HER2）阴性乳腺癌患者在CBC组内的总体死亡风险更高（风险比1.882，95% CI为1.143-3.098），与非CBC组相比也存在差异。本研究发现，乳腺癌患者发展CBC与生存率无关，但在原发性乳腺癌诊断后早期发展CBC或HR阳性/ERBB2阴性乳腺癌患者发展CBC与生存相关。这些结果为考虑对侧预防性乳腺切除术的患者提供了有价值的信息。

Contralateral breast cancer (CBC) is the most frequently diagnosed primary cancer in patients with breast cancer. Although many studies have reported survival after the development of CBC, results have been inconsistent.To investigate whether the development of CBC is associated with survival among patients with breast cancer.This cohort study was conducted at the Asan Medical Center, Korea, among patients who were diagnosed with primary unilateral, nonmetastatic, stage 0 to III breast cancer between 1999 and 2013 and followed up through 2018. The median (IQR) follow-up was 107 (75-143) months. Patients were categorized into CBC and no-CBC groups by whether they developed CBC during the follow-up period. Data were analyzed from November 2021 to March 2023.Development of CBC.Survival rates of CBC and no-CBC groups were compared using a time-dependent Cox proportional hazard model in the entire study population and in subgroup analyses by interval of CBC development and subtype of the primary breast cancer.Among 16 251 patients with breast cancer (all Asian, specifically Korean; mean [SD] age, 48.61 [10.06] years), 418 patients developed CBC. There was no significant difference in overall survival between CBC and no-CBC groups (hazard ratio, 1.166; 95% CI, 0.820-1.657). Patients who developed CBC within 1.5 years after the surgery of the primary breast cancer had a higher risk for overall death during the study period (hazard ratio, 2.014; 95% CI, 1.044-3.886), and those who developed CBC after 1.5 years showed no significant difference in survival compared with the no-CBC group. Patients with hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (ERBB2, formerly HER2)-negative breast cancer had a higher risk for overall death in the CBC group (hazard ratio, 1.882; 95% CI, 1.143-3.098) compared with the no-CBC group.This study found that development of CBC in patients with breast cancer was not associated with survival but that early development of CBC after diagnosis of the primary breast cancer or development of CBC in patients with HR-positive/ERBB2-negative breast cancer was associated with survival. These results may provide valuable information for patients seeking advice on opting for contralateral prophylactic mastectomy.