Thyroid cancer and pesticide use in a Central California agricultural area: a case control study

ABSTRACT: Few studies have examined the environmental factors that influence risk of thyroid cancer. We performed a case-control study utilizing thyroid cancer cases from the California Cancer Registry (1999-2012) and controls sampled in a population-based manner. Study participants resided in one of three central California agricultural counties and were included if they were diagnosed with thyroid cancer, lived in the study area at their time of diagnosis, and were ≥35 years of age. Controls were recruited from the same area and eligible to participate if they were ≥35 years of age and had been living in California for at least 5 years prior to the interview. We examined residential exposure to 29 agricultural use pesticides, known to cause DNA damage in vitro or are known endocrine disruptors. We employed a validated GIS-based system which combines California state mandated pesticide use reporting data, land-use surveys, and geocoded residential addresses to generate exposure estimates for each participant. Our sample included 2067 cases and 1003 controls. In single pollutant models and within a 20-year exposure period, 10 out of 29 selected pesticides were associated with thyroid cancer, including several of the most applied pesticides in the USA such as paraquat dichloride (OR: 1.46, CI: 1.23-1.73), glyphosate (OR: 1.33, CI: 1.12-1.58) and oxyfluorfen (OR: 1.21, CI: 1.02-1.43). Risk of thyroid cancer increased proportionately to the total number of pesticides subjects were exposed to 20 years before diagnosis or interview. In all models, paraquat dichloride was consistently associated with thyroid cancer. Our study provides first evidence in support of the hypothesis that residential pesticide exposure from agricultural applications is associated with an increased risk of thyroid cancer.

摘要：目前针对影响甲状腺癌发病风险的环境因素的相关研究较为匮乏。本研究依托加州癌症登记处（California Cancer Registry）1999-2012年收录的甲状腺癌病例，结合人群抽样选取的对照人群，开展了一项病例对照研究（case-control study）。研究对象均居住于加州中部三个农业县，纳入标准为：确诊甲状腺癌、诊断时居住于本研究区域、年龄≥35岁。对照人群从同一区域招募，合格参与条件为：年龄≥35岁，且于访谈前至少已在加州居住满5年。本研究聚焦29种农业用农药的居住暴露风险，这些农药或在体外可引发DNA损伤，或为已证实的内分泌干扰物。研究采用了一套经过验证的基于地理信息系统（Geographic Information System，GIS）的分析系统，该系统整合了加州法定强制上报的农药使用数据、土地利用调查结果以及地理编码的居住地址信息，为每位研究对象生成暴露水平评估值。本研究最终纳入2067例甲状腺癌病例与1003例对照人群。在单污染物模型以及20年暴露周期的分析中，29种目标农药中有10种与甲状腺癌发病风险显著相关，其中包括美国应用最广泛的数种农药，如百草枯二氯化物（比值比（Odds Ratio，OR）：1.46，95%置信区间（Confidence Interval，CI）：1.23~1.73）、草甘膦（OR：1.33，CI：1.12~1.58）以及乙氧氟草醚（OR：1.21，CI：1.02~1.43）。甲状腺癌发病风险随研究对象在诊断或访谈前20年所暴露的农药总数量呈比例升高。在所有分析模型中，百草枯二氯化物均与甲状腺癌发病风险存在持续稳定的关联。本研究首次提供了证据，支持“农业施用过程产生的居住性农药暴露与甲状腺癌发病风险升高相关”这一假说。