据我们所知，在切尔诺贝利核事故后，尚无完整的基于整体人群的研究关于甲状腺乳头状癌（PTC）患者发展第二原发恶性肿瘤的风险。本研究旨在研究切尔诺贝利灾难后PTC患者第二原发癌的风险。该研究是在白俄罗斯共和国进行的一项回顾性队列研究，时间跨度为31年，评估了具有原发PTC和第二恶性肿瘤的患者。该研究采用了白俄罗斯癌症登记处的个人数据，并且只纳入了第二原发癌进行分析。观察时间段为1990年1月1日至2021年12月31日，以确立第二原发恶性肿瘤。为了进行分析，同步和间歇性肿瘤被分为一个组（第二原发癌组）。如果患者有超过2个肿瘤，将观察其是否发展为第二个肿瘤，随后是否发展为第三个肿瘤。计算人年数的起点是甲状腺癌诊断日期。计算人年数的终点是第二原发恶性肿瘤的诊断日期、患者最后一次就诊日期、死亡日期或2021年12月31日（研究期末）。使用标准化发病率计算PTC患者第二原发恶性肿瘤的发病率。在本研究中，共纳入了30568名原发PTC患者，其中2820人（占9.2%）发展为第二原发恶性肿瘤（2204名女性和616名男性）。在原发癌时，所有患者的平均（标准差）年龄为53.9（12.6）岁，第二个癌症时的平均（标准差）年龄为61.5（11.8）岁。总体而言，所有肿瘤类型的标准化发病率比（SIR）具有统计学显著性（1.25，95% CI，1.21-1.30），包括实体恶性肿瘤（1.20，95% CI，1.15-1.25）和所有白血病（1.61，95% CI，2.17-2.13） 。在PTC后的女性中，消化系统癌症（466例[21.1%]）、生殖器官癌症（376例[17.1%]）和乳腺癌（603例[27.4%]）是最常见的第二原发肿瘤。在男性中，胃肠道肿瘤（146例[27.7%]）、泌尿系统肿瘤（139例[22.6%]）和泌尿道肿瘤（139例[22.6%]）是最常见的。泌尿道癌症（307例[10.9%]）和胃肠道肿瘤（612例[21.4%]）是最常见的第二原发肿瘤。这项队列研究报告了切尔诺贝利灾难后31年内男性和女性实体性继发肿瘤发病率的增加。此外，乳腺、结肠、直肠、间皮组织、眼睛、附件、脑膜和肾上腺等第二原发肿瘤以及卡波西肉瘤的发病率显著增加。这些数据可能对此队列患者的随访有早期发现继发恶性肿瘤的影响。

To our knowledge, there are no complete population-based studies of the risks of developing second malignant tumors after papillary thyroid carcinoma (PTC) in patients following the Chernobyl nuclear accident.To study the risk of second primary cancers in patients with PTC after the Chernobyl disaster.This was a retrospective cohort study conducted in the Republic of Belarus over a 31-year time frame evaluating patients with primary PTC and second malignant tumors. Personal data from the Belarussian Cancer Registry were used in the investigation, and only second primary cancers were included in the analysis. Patients were observed from January 1, 1990, to December 31, 2021, for the establishment of second primary malignant tumors.For analysis, synchronous and metachronous tumors were grouped into 1 group (second primary cancer group). If the patient had more than 2 cancers, they were observed until development of a second tumor and, subsequently, the development of a third tumor. The starting point for calculating the number of person-years was the date of thyroid cancer diagnosis. The end point for calculating the number of person-years was the date of diagnosis of the second primary malignant tumor, the date of death, the date of the last visit of the patient, or December 31, 2021 (the end the of study period). The incidence of a second primary malignant tumor with PTC was calculated for the study groups using standardized incidence ratios.Of the 30 568 patients with a primary PTC included in this study, 2820 (9.2%) developed a second malignant tumor (2204 women and 616 men); the mean (SD) age of all patients at time of the primary cancer was 53.9 (12.6) years and at time of the secondary cancer was 61.5 (11.8) years. Overall, the standardized incidence ratio was statistically significant for all types of cancer (1.25; 95% CI, 1.21-1.30), including solid malignant tumors (1.20; 95% CI, 1.15-1.25) and all leukemias (1.61; 95% CI, 2.17-2.13). Cancers of the digestive system (466 cases [21.1%]), genital organs (376 cases [17.1%]), and breasts (603 cases [27.4%]) were the most prevalent second primary tumors in women following PTC. Second primary tumors of the gastrointestinal tract (146 cases [27.7%]), genitourinary system (139 cases [22.6%]), and urinary tract (139 cases [22.6%]) were the most prevalent in men. Urinary tract cancers (307 cases [10.9%]) and gastrointestinal tumors (612 cases [21.4%]) were the most prevalent second primary tumors overall.This cohort study reports the increased incidence of solid secondary tumors in men and women over a 31-year time frame after the Chernobyl disaster. Moreover, there was a statistically significant increased risk of second tumors of the breast, colon, rectum, mesothelium, eye, adnexa, meninges, and adrenal glands as well as Kaposi sarcoma. These data might have an effect on the follow-up of this cohort of patients to detect secondary malignant tumors at an early stage.