中国女性人乳头瘤病毒感染状况及高危型别分布的Meta分析

目的分析人乳头瘤病毒(human papillomavirus,HPV)在我国不同地区妇女中的感染情况及高危型别分布,以期为制定有效的地区宫颈癌防治策略及HPV疫苗的研制提供科学的基础数据。方法通过检索查询文献,综合分析并评价2011年7月前在国内发表的有关HPV在宫颈组织中感染及高危型别分布的相关研究。结果 HPV在我国普通女性中的感染率为15.71%,低于宫颈病变患者(15.71%vs82.43%,P0.05)。北方地区高危型HPV的平均感染率高于南方(41.57%vs14.81%,P0.05),少数民族自治区高危型HPV的平均感染率高于其他省市(56.36%vs 17.11%,P0.05)。全国范围内前6位常见高危型HPV分布依次为:HPV-16、HPV-52、HPV-58、HPV-33、HPV-18、HPV-31型。HPV-16型是我国最为常见的感染型别,其他型别在不同地区及人群中的分布有一定差异。结论 HPV的感染率及高危型别分布在我国不同地区及不同人群中有一定差异,HPV-16、HPV-52和HPV-58型是中国特有的优势感染型别。     

高危型HPV持续感染在宫颈病变中的分布及其影响因素分析

目的 探讨高危型人乳头瘤病毒(HPV)持续感染在宫颈病变中的分布及其影响因素.方法 选取1388例液基细胞学检查异常者进行宫颈病理组织学检查,同时进行高危型HPV检测并随访,分析不同类型HPV感染的分布情况,以及患者的年龄、性伴侣及宫颈病变的家族史情况.结果 1388例患者中,272例为宫颈炎,936例为宫颈上皮内瘤变(CIN),180例为宫颈癌;宫颈炎患者高危型HPV持续感染率为0.74％,低于其他宫颈病变患者(P﹤0.05).222例高危型HPV持续感染患者中,HPV16、HPV18和HPV58的比例分别为53.60％、22.97％和10.36％;宫颈病变患者中高危型HPV检出较多的亚型分别为HPV16、HPV18和HPV58.初次性行为年龄﹤20岁、性伴侣≥2个和有宫颈癌家族史的患者,其高危型HPV持续感染率分别为21.96％、22.94％和21.20％,高于初次性行为年龄≥20岁、性伴侣1个和无宫颈癌家族史患者的13.33％、13.30％和15.2％(P﹤0.05);合并生殖道炎症的患者,其高危型HPV持续感染率为19.17％,高于无生殖道炎症的患者(P﹤0.05).Logistic回归分析结果显示:初次性行为年龄是高危型HPV持续感染的保护因素(OR=0.576,95％CI:0.576～0.817);性伴侣数量(OR=2.188,95％CI:1.647～2.907)和生殖道炎症(OR=1.904,95％CI:1.214～2.986)是高危型HPV持续感染的危险因素.结论 高危型HPV持续感染主要以HPV16、HPV18和HPV58为主,其不仅与宫颈病变有关,还与患者的初次性行为年龄、性伴侣数量和生殖道炎症有一定的关系.     

宫颈腺癌和宫颈鳞癌中HPV型别感染及其与发病年龄的关系：一项来自多中心的研究

[目的]探讨宫颈鳞癌和宫颈腺癌中HPV型别感染及其与发病年龄的关系.[方法]纳入来自一项多中心临床研究的宫颈腺癌标本32例和鳞癌标本630例.采用三明治技术进行蜡块切片、SPF10-PCR技术进行DNA扩增,使用反向杂交线型探针检测技术(LiPA)的方法进行HPV分型;对所有切片进行病理阅片和诊断,分析宫颈鳞癌和宫颈腺癌标本的HPV分布情况.[结果]宫颈腺癌和宫颈鳞癌标本中,HPV阳性率分别为53.1％(17/32)和97.6％(615/630).宫颈腺癌和鳞癌中高危HPV型别的阳性率分别为50.0％和96.0％(P＜0.001),低危HPV型别的阳性率分别为3.1％和1.7％(P=0.451).鳞癌和腺癌中HPV-16、HPV-18均为主要型别,HPV-16在宫颈腺癌和鳞癌中的阳性率分别为15.6％和76.7％(P＜0.001),HPV-18阳性率分别为25.0％和7.8％(P=-0.002).感染HPV-16和HPV-18对宫颈鳞癌的发病年龄提前具有显著性意义(OR=0.33,0.21,P均＜0.001).[结论]HPV-16和HPV-18为宫颈鳞癌和腺癌中的主要HPV型别.鳞癌中HPV-16和HPV-18感染会导致患者的发病年龄提前.     

高危型HPV阳性细胞学阴性维吾尔族妇女的分流管理

目的 统计≥30岁维吾尔族妇女不同型别人乳头瘤病毒(human papillomavivus,HPV)感染和宫颈细胞学检查结果,分析不同型别HPV感染发生高度宫颈病变(≥CIN2)的风险,为规范化管理未发生宫颈病变和HPV阳性的妇女提供理论依据.方法 收集2012-01-01-2014-02-28新疆维吾尔自治区人民医院妇产科不同型别HPV感染且宫颈细胞学检查未见异常的维吾尔族妇女199例,根据不同HPV型别进行分组,常规全部行阴道镜检查,行宫颈多点活检组织病理学检查,根据病检结果分析各个型别宫颈高度病变的患病率,运用Logistic回归分析不同型别HPV妇女发生高度宫颈病变的风险.结果 199例宫颈细胞学检查未见异常,但HPV分型检测15种高危型HPV阳性的维吾尔族妇女中感染位居前5位的为HPV16、58、52、53和31型.其中高度宫颈病变的患病率为18.59％(37/199),HPV阳性的各个型别中诊断≥CIN2级病变有HPV 16、58、52、31和18型,HPV16型阳性患者发生≥CIN2级病变的患病率为38.48％(20/58),HPV58型阳性的患病率为30.23％(13/43),HPV52型的患病率为5.90％(2/34),HPV31型阳性的患病率为3.70％(1/27),HPV18型阳性的患病率为11.11％(1/9).HPV16型感染发生≥CIN2级的危险是无HPV16型感染者的3.839倍,95％CI为1.829～8.060,P＜0.001;HPV58型感染发生≥CIN2级的危险是无HPV58型感染者的2.365倍,95％CI为1.476～7.669,P=0.004.结论 对于≥30岁维吾尔族妇女宫颈细胞学检查未见异常但高危型HPV阳性者尤其是HPV16和58型阳性者,发生宫颈高度病变的风险较高,应行阴道镜检查,必要时做活检.     

基因芯片技术在德州市女性宫颈HPV感染中的应用研究

目的：了解德州市女性人乳头瘤病毒（human papilloma virus,HPV）感染状况及HPV病毒基因型分布,为宫颈癌筛查提供科学依据。方法使用导流杂交基因芯片技术,对2008年10月至2013年7月期间送检的德州市人民医院3006例宫颈分泌物标本进行HPV基因分型,对各型检出率、年龄分布及多重感染率进行统计分析。结果 HPV总检出率为17．80％（535/3006）,高危型中以 HPV-16、HPV-52、HPV-68检出率最高,分别为3．20％、1．30％、1．26％;低危型中以HPV-6、HPV-11多见,检出率分别为1．50％、1．13％。多重感染共79例,占总感染的14．77％（79/535）,其中二重感染60例（11．21％）、三重感染14例（2．61％）、四重感染5例（0．93％）。HPV感染在16～25岁、26～35岁、36～45岁、46～55岁、56～65岁年龄组中,阳性率分别为16．20％、16．70％、18．20％、16．90％、38．40％,HPV阳性率在56～65岁组达到高峰。结论高危型HPV-16、HPV-52、HPV-68及低危型HPV-6、HPV-11是德州女性宫颈HPV感染的主要基因型别,多重感染较常见,感染人群集中于老年组。导流杂交基因芯片技术一次可检测21种HPV基因型别,特异性强,敏感性高,可应用于宫颈细胞标本HPV感染的检测。     

广元及周边地区宫颈疾病妇女人乳头状瘤病毒感染现状分析

目的分析广元地区宫颈疾病妇女人乳头状瘤病毒（HPV）感染的现状。方法选取2012年10月11日至2013年6月17日间门诊及住院就诊的1260名患宫颈疾病患者。采集患者的宫颈脱落细胞标本,应用导流杂交基因分型技术（HybriMax）对其进行HPV检测和基因分型。分析广元地区宫颈疾病感染HPV的概率、高危型HPV（HR-HPV）的感染率,以及比邻地区HPV亚型的分布现状。结果宫颈疾病HPV感染率为36.6%,重叠感染率为13.4%,高危型（HR-HPV）感染率为47.5%,低危型（LR-HPV）感染率为27.9%,HR-HPV感染率高于LR-HPV感染率。排在前5位的感染型为HPV-58、52、16、53、33;人群HPV年龄段总感染率在≤24岁组出现高峰,而后又在35～39岁组出现高峰,45～49岁组出现低谷,≥60岁出现升高,≥60岁组HPV感染率最高。宫颈炎症患者感染HPV类型谱以高危型HPV-16、58及低危型HPV 11为主,宫颈不典型增生患者感染HPV类型谱以高危型HPV-16、52、58为主,宫颈癌患者HPV类型谱以高危型HPV-16为主。结论广元地地宫颈疾病妇女人乳头状瘤病毒（HPV）感染现状为高感染率和高重叠感染率,HPV的亚型不同,且不同地区HPV亚型的分布也不同。     

人乳头状瘤病毒感染及病毒载量与宫颈病变的相关性研究

目的：研究高危型人乳头状瘤病毒感染及病毒载量与宫颈病变的关系。方法：对774例研究对象采用第二代杂交捕获试验（HC—Ⅱ）进行宫颈脱落细胞的HPV-DNA定量检测。分析不同程度宫颈病变的HPV感染情况,并根据HPV病毒载量将所有检测对象分为四组,阴性（RLU／CO〈1．0）、低载量（1．0≤RLU／CO〈10）、中载量（10≤RLU／CO〈100）、高载量（RLU／CO≥100）,采用非条件多项式logistic回归分析病毒载量与宫颈病变级别的关系。结果：在检测的774例研究对象中,对照组、宫颈上皮内瘤变（cervical intraepithelial neoplasia,CIN）Ⅰ、CINⅡ、CINⅢ和浸润性宫颈癌患者的HPV感染率分别为21．29％、82．35％、80．00％、90．16％和86．67％。对照组高危型HPV感染率明显低于CIN和浸润性宫颈癌患者,差异有统计学意义,P〈0．01;HPV阳性者患CIN的风险是阴性者的24．96倍（95％CI：13．20～47．18）,患浸润性宫颈癌的风险是HPV阴性者的24．03倍（95％CI：12．01～48．09）。在不同级别宫颈病变中,CINI组的低病毒载量患者占11．67％,高载量占41．18％,OR值为23．84（95％CI：5．96～95．33）,P〈0．001;而在CINⅢ组中62．30％的患者呈高病毒载量,OR值达64．70（95％CI：25．98～161．20）,P〈0．001。结论：高危型HPV感染与CIN和浸润性宫颈癌的发生密切相关;宫颈高危型HPV病毒载量是影响宫颈病变严重程度的危险因素。     

高危型人乳头瘤病毒DNA检测在南京地区10 221例宫颈癌前病变筛查中的应用效果分析

目的 探讨南京地区高危型人乳头瘤病毒（HR HPV） DNA检测用于宫颈癌前病变筛查的效果。方法 收集南京地区10 221例女性体检的宫颈脱落细胞标本,运用多重荧光PCR技术进行HR-HPV DNA检测（包括12种不分型、HPV-16、HPV-18）,并结合同时送检的薄层液基细胞学（TCT）和187例阴道镜宫颈活检病理结果进行比较分析。结果 10 221例受检标本检出HR-HPV感染1037例（10.15％）;HPV不分型12种为最常见感染型别,占7.86％。＜45岁与≥45岁人群比较,HR-HPV感染率显著降低,差异有统计学意义（P=0.020）;随着年龄增加,HR-HPV 感染者中发生高度宫颈上皮内瘤变（CIN）的比例增加,≥45岁与＜45岁患者比较,差异有统计学意义（P=0.006）。TCT检测显示,细胞学异常组的HR-HPV感染率为54.22％（199／367）,显著高于细胞学正常或慢性炎症组的8.50％（838／9854）,差异有统计学意义（P=0.000）。相比HPV不分型12种,16型和18型与细胞病变级别增加的关系更加密切（P=0.0000）;随着病变病理级别增高,16型阳性率增高,即16型感染与CIN级别增加有关（P=0.003）。结论 HR-HPV筛查可以考虑提前至25岁,且45岁以上女性作为HR-HPV高发人群应密切随访;HPV-16感染在诱发细胞高度病变进而进展为宫颈癌前病变中起重要作用;HR-HPV DNA检测可作为有效的初筛工具应用于宫颈癌前病变高风险人群的风险分层管理中。     

人乳头瘤病毒感染与亚洲人膀胱癌罹患危险度的Meta分析

[目的]探讨人乳头瘤病毒（HPV）感染与亚洲人膀胱癌罹患之间的危险性。[方法]计算机检索Pubmed、CNKI数据库、万方数据库,同时利用文献追溯等途径收集1989年1月至2011年3月国内外公开发表的有关HPV感染与亚洲人膀胱癌患病的相关文献,同时检索相关引用文献。应用Meta分析对其进行综合评价。[结果]共31篇文献符合纳入标准,其中病例—对照研究18篇。亚洲膀胱癌患者中HPV总的感染率为35.67%（95%CI：33.43%～37.97%）,其中高危型HPV感染率为34.29%（95%CI：31.77%～36.87%）。亚洲人膀胱癌患者膀胱癌组织中HPV的检出率主要受到HPV感染型别和发表年限的影响。而中国大陆膀胱癌患者中,HPV的感染率为47.27%（95%CI：44.12%～50.44%）,显著高于亚洲平均水平（P〈0.001）。固定效应模型计算结果显示,亚洲人中HPV感染对膀胱癌罹患关联的OR值为5.17（95%CI：3.52～7.60）,且主要受到HPV感染型别的影响。[结论]亚洲人中HPV感染,尤其是高危型HPV感染,可能会增加膀胱癌罹患的危险性。     

中国大陆女性体检人群中人乳头瘤病毒型别感染率及九价疫苗中HPV各型别分布的系统评价

目的：探讨人乳头瘤病毒(human papillomavirus, HPV)在我国大陆女性体检人群中感染及型别分布特征,为体检人群接种九价HPV疫苗提供科学依据。方法：采用系统评价法综合评价检索1995年1月1日～2016年12月31日在Pubmed、Medline、知网、维普和万方数据库收录的所有关于中国正常女性人群中发表的有关HPV感染及型别分布的相关研究。由 2 位研究者独立筛选文献、提取数据资料和评价纳入研究的文献质量,采用Stata 12.0 软件进行分析。结果：研究共纳入19篇文献,总人数为504 566人;随机效应模型结果显示,我国正常体检女性人群中HPV的感染率为16.18%[95%CI(14.16,18.20)%],高危型、低危型的感染率分别为12.95%和3.28%,九价疫苗中高危型和低危型的感染率为10.59%和1.56%,而九价疫苗中所有型的感染率是12.15%[95%CI(10.18,14.13)%],其中大陆体检女性人群中比较常见的型别是HPV16/52/58/33/18/68。七大区的HPV感染率及型别均不同,正常体检人群女性中总HPV、高危型以及低危型的感染率最高的是华东地区,分别为17.54%[95%CI(16.82,18.27)%]、14.17%[95%CI(13.50,14.83)%]、3.75%[95%CI(2.11,6.11)%],总HPV感染率最低的是西北8.79%[95%CI(7.47,10.26)%],高危型感染率最低的是西南地区3.04%[95%CI(6.80,8.70)%],低危型感染率最低的是西南地区0.14%[95%CI(0.02,0.49) %];九价HPV疫苗中高危型的感染率最高的华中和华东地区分别为11.36%[95%CI(9.33,13.40)%]和11.36%[95%CI(10.75,11.97)%],最低的是东北地区为7.83%[95%CI(7.18,8.51)%];九价HPV疫苗中低危型的感染率最高的华北地区为3.50%[95%CI(1.93,5.80)%],感染率最低的是华中地区为0.30% [95%CI(0.06,0.87)%];九价HPV疫苗中所有型的感染率最高的华北地区为12.75%[95%CI(9.64,16.42)%],最低是东北地区为8.34%[95%CI(7.67,9.03)%]。正常体检女性人群中HPV总的感染率、高危型和低危型感染率均是南方高于北方,差异有统计学意义;九价疫苗的低危型感染率则相反,南北方感染的HPV型别以及感染率均不同,而九价疫苗中高危型及全部型别的南北方感染率差异无统计学意义。经非条件Logistic 回归分析,使用GP5+/6+引物系统检测出的HPV调整感染率显著高于其它引物系统(P<0.001);总HPV调整感染率随发表年限增加而增加(P<0.001)。结论：中国大陆地区健康体检的女性人群中HPV的感染率较高,常见的型别为HPV16/52/58/33/18,不同地区型别分布及感染率不同其中华中地区最高,西北地区最低,且南北方存在差异。而在体检人群中接种九价HPV疫苗其防治效果明显,但是还需要进行宫颈癌的筛查。 受纳入研究的文献检测方法多样性和质量的限制,上述结论尚需要更多研究予以证实。     

Familial cancer and cancer families.

From this brief review is should be evident that the hereditary varieties of common cancers are characterized by a high degree of genetic heterogeneity. The specific types of hereditary cancers can be identified by focusing on the histologic types and sites of involvement, not only of the primary neoplasm, but also of associated neoplasms and associated conditions or stigmata, as well as by focusing on the age of the patient at the time of diagnosis, tumor localization and frequency, and the mode of inheritance. Identification of specific types of hereditary cancers has important utility as a means of isolating homogeneous groups of patients and unaffected relatives for studies aimed at elucidating the mechanisms of carcinogenesis.     

Oral complications of cancer and cancer therapy

Answer questions and earn CME/CNE Oral complications resulting from cancer and cancer therapies cause acute and late toxicities that may be underreported, underrecognized, and undertreated. Recent advances in cancer treatment have led to changes in the incidence, nature, and severity of oral complications. As the number of survivors increases, it is becoming increasingly recognized that the aggressive management of oral toxicities is needed to ensure optimal long‐term oral health and general well‐being. Advances in care have had an impact on previously recognized oral complications and are leading to newly recognized adverse effects. Here, the authors briefly review advances in cancer therapy, including recent advances in surgery, oral care, radiation therapy, hematopoietic cell transplantation, and medical oncology; describe how these advances affect oral health; and discuss the frequent and/or severe oral health complications associated with cancer and cancer treatment and their effect upon long‐term health. Although some of the acute oral toxicities of cancer therapies may be reduced, they remain essentially unavoidable. The significant impact of long‐term complications requires increased awareness and recognition to promote prevention and appropriate intervention. It is therefore important for the primary oncologist to be aware of these complications so that appropriate measures can be implemented in a timely manner. Prevention and management is best provided via multidisciplinary health care teams, which must be integrated and communicate effectively in order to provide the best patient care in a coordinated manner at the appropriate time. CA Cancer J Clin 2012. © 2012 American Cancer Society.     

Present and future state of cancer screening for esophageal cancer and gastric cancer

Recently, endoscopic examinations have played a major role in the diagnosis and treatment in the field of gastroenterology. It is considered that endoscopy would be an important examination for cancer screening of the esophagus and the stomach. However, endoscopic services for cancer screening are in short supply. Furthermore, we have to take the complications and poor economic benefits of endoscopy in to consideration when we apply it as a practical cancer screening system. Thus, an effective primary screening system must be provided for the endoscopic screening of cancer of the esophagus and the stomach. People with a defect in aldehyde dehydrogenase-2(ALDH2)should be distinguished by their facial flushing in drinking and for their high risks of esophageal cancer. In cases with gastric cancer screening by endoscopy, an x-ray study is expected to be a primary screening because of its efficacy. It already has been recommended for population-based screening in Japanese guidelines for gastric cancer screening. In cases with opportunistic screening of gastric cancer, patients should be allowed to choose from several studies such as the x-ray study, direct endoscopy, and the so-called high risk screening of gastric cancer for estimating risks and planning of screening for gastric cancer.     

Endocrine sequelae of cancer and cancer treatments

Introduction Exposure to cancer and its treatments, including chemotherapy and radiotherapy, may result in late adverse effects including endocrine dysfunction. Endocrine disorders are the most commonly reported long-term complications of cancer treatment, especially by adult survivors of childhood cancers. This review will explore the endocrinologic adverse effects from non-endocrine cancer therapies. Methods Searches including various Internet-based medical search engines such as PubMed, Medline Plus, and Google Scholar were conducted for published articles. Results One hundred sixty-nine journal articles met the inclusion criteria. They included case reports, systematic analyses, and cohort reports. Endocrine disorders including hypothalamus dysfunction, hypopituitarism, syndrome of inappropriate anti-diuretic hormone secretion, diabetes insipidus, growth hormone disorders, hyperprolactinemia, gonadotropin deficiency, serum thyroid hormone-binding protein abnormalities, hypothyroidism, hyperthyroidism, hypomagnesium, hypocalcemia, hyperparathyroidism, hyperparathyroidism, adrenal dysfunction, gonadal dysfunction, hypertriglyceridemia, hypercholesterolemia, diabetes mellitus, and glycosuria were identified and their association with cancer therapies were outlined. Discussion/conclusions The journal articles have highlighted the association of cancer therapies, including chemotherapy and radiotherapy, with endocrine dysfunction. Some of the dysfunctions were more often experienced than others. Especially in patients treated with radiotherapy, some endocrinologic disorders were progressive in nature. Implications for cancer survivors Recognition and awareness of endocrine sequelae of cancer treatments may permit for early detection and appropriate follow-up care for cancer survivors, thus improving their overall health and quality of life.     

前列腺癌和乳腺癌的对比性研究

人体一些肿瘤的生长对某些激素有一定的依赖关系,激素阻断可抑制其生长,被称为激素相关性肿瘤,如甲状腺癌、乳腺癌、子宫内膜癌及前列腺癌等.其中前列腺癌和乳腺癌为人群中发病率较高的两种恶性肿瘤,在很多方面均具有类似的特点.将二者在各方面进行对比性研究,有利于总结前列腺癌治疗方案,提高治疗效果.     

Skeletal sequelae of cancer and cancer treatment

Introduction  Survivors of cancer may experience lingering adverse skeletal effects such as osteoporosis and osteomalacia. Skeletal disorders are often associated with advancing age, but these effects can be exacerbated by exposure to cancer and its treatment. This review will explore the cancer and cancer treatment-related causes of skeletal disorders. Methods  We performed a comprehensive search, using various Internet-based medical search engines such as PubMed, Medline Plus, Scopus, and Google Scholar, for published articles on the skeletal effects of cancer and cancer therapies. Results  One-hundred-forty-two publications, including journal articles, books, and book chapters, met the inclusion criteria. They included case reports, literature reviews, systematic analyses, and cohort reports. Skeletal effects resulting from cancer and cancer therapies, including hypogonadism, androgen deprivation therapy, estrogen suppression, glucocorticoids/corticosteroids, methotrexate, megestrol acetate, platinum compounds, cyclophosphamide, doxorubicin, interferon-alpha, valproic acid, cyclosporine, vitamin A, NSAIDS, estramustine, ifosfamide, radiotherapy, and combined chemotherapeutic regimens, were identified and described. Skeletal effects of hyperparathyroidism, vitamin D deficiency, gastrectomy, hypophosphatemia, and hyperprolactinemia resulting from cancer therapies were also described. Discussion/Conclusions  The publications researched during this review both highlight and emphasize the association between cancer therapies, including chemotherapy and radiotherapy, and skeletal dysfunction. Implications for cancer survivors  These studies confirm that cancer survivors experience a more rapid acceleration of bone loss than their age-matched peers who were never diagnosed with cancer. Further studies are needed to better address the skeletal needs of cancer survivors.     

Animal cancer tests and cancer prevention.

The toxicological significance of exposures to synthetic chemicals is examined in the context of exposures to naturally occurring chemicals. We calculate that 99.99% (by weight) of the pesticides in the US diet are chemicals that plants produce to defend themselves (nature's pesticides). Only 52 of these natural pesticides have been tested in high-dose animal cancer tests, and 27 are rodent carcinogens; these 27 are shown to be present in many common foods. The toxicology of synthetic chemicals is compared to that of natural chemicals, which represent the vast bulk of the chemicals to which humans are exposed. It is argued that animals have a broad array of inducible general defenses to combat the changing array of toxic chemicals in plant food and that these defenses are effective against both natural and synthetic toxins. Synthetic toxins (eg, dioxin) are compared to natural chemicals (eg, indole carbinol [in broccoli] and ethanol). The finding that, in high-dose tests, a high proportion of both natural and synthetic chemicals are carcinogens, mutagens, teratogens, and clastogens (30%-50% for each group) calls into question current efforts to use these tests to protect public health by regulating low doses of synthetic chemicals. The administration of chemicals at the maximum tolerated dose in standard animal cancer tests is postulated to increase cell division (mitogenesis), which in turn increases rates of mutagenesis and, thus, carcinogenesis. The animal data are consistent with this mechanism, because a high proportion--about 50%--of all chemicals tested (whether natural or synthetic) are indeed rodent carcinogens.(ABSTRACT TRUNCATED AT 250 WORDS)