Background

It remains unclear whether radiation therapy (RT) has an impact on the development of secondary primary cancer (SC) in rectal cancer (RC) patients, especially within the true pelvis.

Aim

To examine the incidence of SC in a population-based cohort of RC after surgical treatment with or without radiation therapy (RT, NRT).

Patients and Methods

The epidemiological cohort consisting of 13,919 RC patients with primary M0 stage diagnosed between 1998 and 2019 was collected from cancer registry data of Upper Bavaria. Competing risk analyses were conducted regarding the development of SC on 11 687 first malignancies, stratified by RT/NRT. A propensity score (PS) was generated by logistic regression modeling of RT to repeat competing risk analyses on a PS-matched cohort.

Results

The median age (interquartile range) of the epidemiological cohort was 68.9 years (60.4-76.7). About 60.8%, were men, 38.7% had UICC III, 35.8% of tumors were localized lower than 8 cm, 41.3% underwent RT. Only 17.1% of patients older than 80 years at diagnosis received RT. In general, RT patients were 5 years younger than NRT patients (65.9 years [58.0-73.0] vs. 71.3 years [62.4-79.2], P < .0001). The 20-year cumulative incidence of SC was 16.5% in RT and 17.4% in NRT patients (P = .2298). Men with RT had a lower risk of prostate cancer (HR = 0.55, 95%CI [0.34-0.91], P = .0168). In the PS-matched cohort, RT patients had a significantly higher risk of bladder cancer during follow-up (10-year cumulative incidence of 1.1% vs. 0.6% in NRT). The direction of the RT effects in men and women and different tumor sites may cancel each other.

Conclusion

A protective effect of RT in rectal cancer patients on developing prostate SC by half is reproduced. Further analyses studying the long-term SC risks of RT should essentially focus on stratification by sex, and focus on more recent data.

中文翻译：

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直肠癌放射治疗后的继发性原发癌症风险：基于人群的倾向评分匹配队列研究

背景

目前尚不清楚放射治疗 (RT) 是否对直肠癌 (RC) 患者继发原发癌 (SC) 的发展产生影响，尤其是在真骨盆内。

目的

旨在检查基于人群的 RC 队列在手术治疗（联合或不联合放射治疗（RT、NRT））后 SC 的发生率。

患者和方法

流行病学队列由 1998 年至 2019 年间诊断的 13,919 名原发性 M0 期 RC 患者组成，收集自上巴伐利亚州的癌症登记数据。对 11 687 例首发恶性肿瘤的 SC 发展进行了竞争风险分析，按 RT/NRT 分层。通过RT 的逻辑回归模型生成倾向评分 (PS)，以对 PS 匹配的队列重复竞争风险分析。

结果

流行病学队列的中位年龄（四分位距）为 68.9 岁（60.4-76.7）。约 60.8% 为男性，38.7% 患有 UICC III，35.8% 肿瘤局限性低于 8 cm，41.3% 接受 RT。只有 17.1% 诊断时年龄超过 80 岁的患者接受了 RT。一般来说，RT 患者比 NRT 患者年轻 5 岁（65.9 岁 [58.0-73.0] 对比 71.3 岁 [62.4-79.2]，P < .0001）。RT 患者中 SC 的 20 年累积发生率为 16.5%，NRT 患者中 SC 的 20 年累积发生率为 17.4% ( P  = .2298)。接受 RT 的男性患前列腺癌的风险较低（HR = 0.55，95% CI [0.34-0.91]，P  = .0168）。在 PS 匹配队列中，RT 患者在随访期间患膀胱癌的风险显着较高（10 年累积发病率为 1.1%，而 NRT 患者为 0.6%）。男性和女性以及不同肿瘤部位的放疗效果方向可能会相互抵消。

结论

直肠癌患者放疗对前列腺 SC 的保护作用减半。研究 RT 的长期 SC 风险的进一步分析应主要关注按性别分层，并关注更新的数据。