经诊断出表皮默克尔细胞癌（MCC）后，随后的原发性癌症风险尚不确定。为评估在首次表皮默克尔细胞癌诊断后随后的原发性癌症风险，本队列研究分析了《监测、流行病学和结果调查（SEER）计划》的17个登记册的数据，时间跨度为2000年1月1日至2019年12月31日。共鉴定了6146名首次诊断为原发性表皮默克尔细胞癌的患者。主要结果为首次诊断默克尔细胞癌后随后原发性癌症的相对风险和绝对风险，分别通过标准化发病率比（SIR，随后癌症的观察到的与预期的发病例数比率）和超额风险（相对风险与患者在风险期内的人年差异除以），在2000年1月1日至2019年12月31日期间进行数据分析。6146例首次诊断默克尔细胞癌的患者，年龄的中位数（四分位数）为76（66-83）岁，男性3713例（60.4％），占主导地位的种族和民族为非西班牙裔白人（5491例[ 89.3％]）。其中，725例（11.8％）患者出现随后的原发性癌症，SIR为1.28（95％CI，1.19-1.38），超额风险为每10,000人-年57.25。对于MCC后出现的实体肿瘤，皮肤黑素瘤风险增加（SIR为2.36 [95％CI，1.85-2.97]；超额风险为每10,000人年15.27），乳头状甲状腺癌风险增加（SIR为5.26 [95％CI，3.25-8.04]；超额风险为每10,000人年6.16）。对于MCC后的血液系统癌症，非何杰金淋巴瘤风险增加（SIR为2.62 [95％CI，2.04-3.32]；超额风险为每10,000人年15.48）。本队列研究发现，MCC患者随后出现固体肿瘤和血液系统癌症的风险增加。这种风险的增加可能与增加的监测、治疗相关因素或MCC与其他癌症的共同病因有关。有必要开展进一步研究，以探索MCC与其他原发性癌症之间可能存在的共同病因因素。

The risk of subsequent primary cancers after a diagnosis of cutaneous Merkel cell carcinoma (MCC) is not well established.To evaluate the risk of subsequent primary cancers after the diagnosis of a first primary cutaneous MCC.This cohort study analyzed data from 17 registries of the Surveillance, Epidemiology, and End Results (SEER) Program from January 1, 2000, to December 31, 2019. In all, 6146 patients diagnosed with a first primary cutaneous MCC were identified.The primary outcome was the relative and absolute risks of subsequent primary cancers after the diagnosis of a first primary MCC, which were calculated using the standardized incidence ratio (SIR; ratio of observed to expected cases of subsequent cancer) and the excess risk (difference between observed and expected cases of subsequent cancer divided by the person-years at risk), respectively. Data were analyzed between January 1, 2000, and December 31, 2019.Of 6146 patients with a first primary MCC diagnosed at a median (IQR) age of 76 (66-83) years, 3713 (60.4%) were men, and the predominant race and ethnicity was non-Hispanic White (5491 individuals [89.3%]). Of these patients, 725 (11.8%) developed subsequent primary cancers, with an SIR of 1.28 (95% CI, 1.19-1.38) and excess risk of 57.25 per 10 000 person-years. For solid tumors after MCC, risk was elevated for cutaneous melanoma (SIR, 2.36 [95% CI, 1.85-2.97]; excess risk, 15.27 per 10 000 person-years) and papillary thyroid carcinoma (SIR, 5.26 [95% CI, 3.25-8.04]; excess risk, 6.16 per 10 000 person-years). For hematologic cancers after MCC, risk was increased for non-Hodgkin lymphoma (SIR, 2.62 [95% CI, 2.04-3.32]; excess risk, 15.48 per 10 000 person-years).This cohort study found that patients with MCC had an increased risk of subsequently developing solid and hematologic cancers. This increased risk may be associated with increased surveillance, treatment-related factors, or shared etiologies of the other cancers with MCC. Further studies exploring possible common etiological factors shared between MCC and other primary cancers are warranted.