Hydrologic, land cover, and seasonal patterns of waterborne pathogens in Great Lakes tributaries.

Great Lakes tributaries are known to deliver waterborne pathogens from a host of sources. To examine the hydrologic, land cover, and seasonal patterns of waterborne pathogens (i.e. protozoa (2), pathogenic bacteria (4) human viruses, (8) and bovine viruses (8)) eight rivers were monitored in the Great Lakes Basin over 29 months from February 2011 to June 2013. Sampling locations represented a wide variety of land cover classes from urban to agriculture to forest. A custom automated pathogen sampler was deployed at eight sampling locations which provided unattended, flow-weighted, large-volume (120-1630 L) sampling. Human and bovine viruses and pathogenic bacteria were detected by real-time qPCR in 16%, 14%, and 1.4% of 290 samples collected while protozoa were never detected. The most frequently detected pathogens were: bovine polyomavirus (11%), and human adenovirus C, D, F (9%). Human and bovine viruses were present in 16.9% and 14.8% of runoff-event samples (n = 189) resulting from precipitation and snowmelt, and 13.9% and 12.9% of low-flow samples (n = 101), respectively, indicating multiple delivery mechanisms could be influential. Data indicated human and bovine virus prevalence was different depending on land cover within the watershed. Occurrence, concentration, and flux of human viruses were greatest in samples from the three sampling locations with greater than 25% urban influence than those with less than 25% urban influence. Similarly, occurrence, concentration, and flux of bovine viruses were greatest in samples from the two sampling locations with greater than 50 cattle/km2 than those with less than 50 cattle/km2. In seasonal analysis, human and bovine viruses occurred more frequently in spring and winter seasons than during the fall and summer. Concentration, occurrence, and flux in the context of hydrologic condition, seasonality, and land use must be considered for each watershed individually to develop effective watershed management strategies for pathogen reduction.

Effects of dairy slurry on silage fermentation characteristics and nutritive value of alfalfa.

Dairy producers frequently ask questions about the risks associated with applying dairy slurry to growing alfalfa (Medicago sativa L.). Our objectives were to determine the effects of applying dairy slurry on the subsequent nutritive value and fermentation characteristics of alfalfa balage. Dairy slurry was applied to 0.17-ha plots of alfalfa; applications were made to the second (HARV1) and third (HARV2) cuttings during June and July of 2012, respectively, at mean rates of 42,400 ± 5271 and 41,700 ± 2397 L/ha, respectively. Application strategies included (1) no slurry, (2) slurry applied directly to stubble immediately after the preceding harvest, (3) slurry applied after 1 wk of post-ensiled regrowth, or (4) slurry applied after 2 wk of regrowth. All harvested forage was packaged in large, rectangular bales that were ensiled as wrapped balage. Yields of DM harvested from HARV1 (2,477 kg/ha) and HARV2 (781 kg/ha) were not affected by slurry application treatment. By May 2013, all silages appeared to be well preserved, with no indication of undesirable odors characteristic of clostridial fermentations. Clostridium tyrobutyricum, which is known to negatively affect cheese production, was not detected in any forage on either a pre- or post-ensiled basis. On a pre-ensiled basis, counts for Clostridium cluster 1 were greater for slurry-applied plots than for those receiving no slurry, and this response was consistent for HARV1 (4.44 vs. 3.29 log10 genomic copies/g) and HARV2 (4.99 vs. 3.88 log10 genomic copies/g). Similar responses were observed on a post-ensiled basis; however, post-ensiled counts also were greater for HARV1 (5.51 vs. 5.17 log10 genomic copies/g) and HARV2 (5.84 vs. 5.28 log10 genomic copies/g) when slurry was applied to regrowth compared with stubble. For HARV2, counts also were greater following a 2-wk application delay compared with a 1-wk delay (6.23 vs. 5.45 log10 genomic copies/g). These results suggest that the risk of clostridial fermentations in alfalfa silages is greater following applications of slurry. Based on pre- and post-ensiled clostridial counts, applications of dairy slurry on stubble are preferred (and less risky) compared with delayed applications on growing alfalfa.

Serum protein profiling reveals baseline and pharmacodynamic biomarker signatures associated with clinical outcome in mCRC patients treated with chemotherapy ± cediranib.

BACKGROUND: This study evaluated soluble serum proteins as biomarkers to subset patients with metastatic colorectal cancer (mCRC) treated with chemotherapy±cediranib, a vascular endothelial growth factor (VEGF) signalling inhibitor (VEGFi). Exploring biomarkers at pre- and on-treatment may identify patient subgroups showing clinical benefit on cediranib combination. METHODS: Two hundred and seven serum proteins were analysed in 588 mCRC patients at pre- and on-treatment with chemotherapy (FOLFOX/CAPOX)±cediranib 20 mg. Patients were enrolled in the phase III trial HORIZON II. We correlated baseline biomarker signatures and pharmacodynamic (PD) biomarkers with PFS and OS. RESULTS: We identified a baseline signature (BS) of 47 biomarkers that included VEGFA, VEGFD, VEGFR2, VEGFR3 and TIE-2, which defined two distinct subgroups of patients. Patients treated with chemotherapy plus cediranib who had 'high' BS had shorter PFS (HR=1.82, P=0.003) than patients with 'low' BS. This BS did not correlate with PFS of the patients treated with chemotherapy plus placebo. In addition, we identified a profile of 16 PD proteins on treatment associated with PFS (HR=0.58, P<0.001) and OS (HR=0.52, P<0.001) in patients treated with chemotherapy plus cediranib. This PD profile did not correlate with PFS and OS in patients treated with chemotherapy plus placebo. CONCLUSIONS: Serum proteins may represent relevant biomarkers to predict the outcome of patients treated with VEGFi-based therapies. We report a BS and PD biomarkers that may identify mCRC patients showing increased benefit of combining cediranib with chemotherapy. These exploratory findings need to be validated in future prospective studies.

Human and bovine viruses in the Milwaukee River watershed: hydrologically relevant representation and relations with environmental variables.

To examine the occurrence, hydrologic variability, and seasonal variability of human and bovine viruses in surface water, three stream locations were monitored in the Milwaukee River watershed in Wisconsin, USA, from February 2007 through June 2008. Monitoring sites included an urban subwatershed, a rural subwatershed, and the Milwaukee River at the mouth. To collect samples that characterize variability throughout changing hydrologic periods, a process control system was developed for unattended, large-volume (56-2800 L) filtration over extended durations. This system provided flow-weighted mean concentrations during runoff and extended (24-h) low-flow periods. Human viruses and bovine viruses were detected by real-time qPCR in 49% and 41% of samples (n=63), respectively. All human viruses analyzed were detected at least once including adenovirus (40% of samples), GI norovirus (10%), enterovirus (8%), rotavirus (6%), GII norovirus (1.6%) and hepatitis A virus (1.6%). Three of seven bovine viruses analyzed were detected including bovine polyomavirus (32%), bovine rotavirus (19%), and bovine viral diarrhea virus type 1 (5%). Human viruses were present in 63% of runoff samples resulting from precipitation and snowmelt, and 20% of low-flow samples. Maximum human virus concentrations exceeded 300 genomic copies/L. Bovine viruses were present in 46% of runoff samples resulting from precipitation and snowmelt and 14% of low-flow samples. The maximum bovine virus concentration was 11 genomic copies/L. Statistical modeling indicated that stream flow, precipitation, and season explained the variability of human viruses in the watershed, and hydrologic condition (runoff event or low-flow) and season explained the variability of the sum of human and bovine viruses; however, no model was identified that could explain the variability of bovine viruses alone. Understanding the factors that affect virus fate and transport in rivers will aid watershed management for minimizing human exposure and disease transmission.

Prognostic/predictive value of 207 serum factors in colorectal cancer treated with cediranib and/or chemotherapy.

BACKGROUND: The prognostic and predictive value of multiple serum biomarkers was evaluated using samples from a randomised phase III study (HORIZON II) investigating chemotherapy with or without cediranib in metastatic colorectal cancer (mCRC). METHODS: Baseline levels of 207 protein markers were measured in serum samples from 582 HORIZON II (FOLFOX/XELOX plus cediranib 20 mg (n=330) or placebo (n=252)) patients. Median baseline values of each biomarker were used to categorise patients as high or low. Markers were then assessed for their association with efficacy, defined by progression-free survival (PFS) and overall survival (OS). A generalised boosted regression model identified markers of particular interest. RESULTS: Correlation of protein levels with PFS and OS suggested that multiple factors had a prognostic value, independent of treatment arm, including IL-6, IL-8, C-reactive protein (CRP), ICAM-1 and carcinoembryonic antigen (CEA). Among the angiogenesis regulators, low levels of vascular endothelial growth factor (VEGF), VEGF-D, VEGFR-1, VEGFR-3, NRP1 and Tie-2 correlated with better outcome. CONCLUSION: This large data set generated using serum samples from mCRC patients treated with chemotherapy and VEGF inhibitors, defines baseline characteristics for 207 serum proteins. Multiple prognostic factors were identified that could be disease related or predict which patients derive most benefit from 5-fluorouracil (5-FU)-based chemotherapy, meriting further exploration in prospective studies.

Recent skin self-examination and doctor visits in relation to melanoma risk and tumour depth.

BACKGROUND: Little is known about the potential benefit of skin self-examination for melanoma prevention and early detection. OBJECTIVES: To determine whether skin self-examination is associated with reduced melanoma risk, self-detection of tumours, and reduced risk of deeper melanomas. METHODS: We used data from a population-based case-control study (423 cases, 678 controls) to assess recent skin self-examination in relation to self-detection, melanoma risk and tumour depth ( ≤1 mm; > 1 mm). Logistic regression was used to estimate odds ratios (ORs) and confidence intervals (CIs) for associations of interest. RESULTS: Skin self-examination conducted 1-11 times during a recent year was associated with a possible decrease in melanoma risk (OR 0·74; 95% CI 0·54-1·02). Melanoma risk was decreased for those who conducted skin self-examination and saw a doctor (OR 0·52; 95% CI 0·30-0·90). Among cases, those who examined their skin were twice as likely to self-detect the melanoma (OR 2·23; 95% CI 1·47-3·38), but self-detection was not associated with shallower tumours. Tumour depth was reduced for those who conducted skin self-examination 1-11 times during a recent year (OR 0·39; 95% CI 0·18-0·81), but was not influenced by seeing a doctor, or by conducting skin self-examination and seeing a doctor. CONCLUSIONS: Risk of a deeper tumour and possibly risk of melanoma were reduced by skin self-examination 1-11 times annually. Melanoma risk was markedly reduced by skin self-examination coupled with a doctor visit. We cannot, however, exclude the possibility that our findings reflect bias or confounding. Additional studies are needed to elucidate the potential benefits of skin self-examination for melanoma prevention and early detection.

Measuring and mitigating inhibition during quantitative real time PCR analysis of viral nucleic acid extracts from large-volume environmental water samples.

Naturally-occurring inhibitory compounds are a major concern during qPCR and RT-qPCR analysis of environmental samples, particularly large volume water samples. Here, a standardized method for measuring and mitigating sample inhibition in environmental water concentrates is described. Specifically, the method 1) employs a commercially available standard RNA control; 2) defines inhibition by the change in the quantification cycle (C(q)) of the standard RNA control when added to the sample concentrate; and 3) calculates a dilution factor using a mathematical formula applied to the change in C(q) to indicate the specific volume of nuclease-free water necessary to dilute the effect of inhibitors. The standardized inhibition method was applied to 3,193 large-volume water (surface, groundwater, drinking water, agricultural runoff, sewage) concentrates of which 1,074 (34%) were inhibited. Inhibition level was not related to sample volume. Samples collected from the same locations over a one to two year period had widely variable inhibition levels. The proportion of samples that could have been reported as false negatives if inhibition had not been mitigated was between 0.3% and 71%, depending on water source. These findings emphasize the importance of measuring and mitigating inhibition when reporting qPCR results for viral pathogens in environmental waters to minimize the likelihood of reporting false negatives and under-quantifying virus concentration.

New mathematical approaches to quantify human infectious viruses from environmental media using integrated cell culture-qPCR.

Quantifying infectious viruses by cell culture depends on visualizing cytopathic effect, or for integrated cell culture-PCR, attaining confidence a PCR-positive signal is the result of virus growth and not inoculum carryover. This study developed mathematical methods to calculate infectious virus numbers based on viral growth kinetics in cell culture. Poliovirus was inoculated into BGM cell monolayers at 10 concentrations from 0.001 to 1000 PFU/ml. Copy numbers of negative-strand RNA, a marker of infectivity for single-stranded positive RNA viruses, were measured over time by qRT-PCR. Growth data were analyzed by two approaches. First, data were fit with a continuous function to estimate directly the initial virus number, expressed as genomic copies. Such estimates correlated with actual inoculum numbers across all concentrations (R(2)=0.62, n=17). Second, the length of lag phase appeared to vary inversely with inoculum titers; hence, standard curves to predict inoculum virus numbers were derived based on three definitions of lag time: (1) time of first detection of (-)RNA, (2) second derivative maximum of the fitted continuous function, and (3) time when the fitted curve crossed a threshold (-)RNA concentration. All three proxies yielded standard curves with R(2)=0.69-0.90 (n=17). The primary advantage of these growth kinetics approaches is being able to quantify virions that are unambiguously infectious, a particular advantage for viruses that do not produce CPE.

Concentrating Toxoplasma gondii and Cyclospora cayetanensis from surface water and drinking water by continuous separation channel centrifugation.

AIMS: To evaluate the effectiveness of continuous separation channel centrifugation for concentrating Toxoplasma gondii and Cyclospora cayetanensis from drinking water and environmental waters. METHODS AND RESULTS: Ready-to-seed vials with known quantities of T. gondii and C. cayetanensis oocysts were prepared by flow cytometry. Oocysts were seeded at densities ranging from 1 to 1000 oocysts l(-1) into 10 to 100 l test volumes of finished drinking water, water with manipulated turbidity, and the source waters from nine drinking water utilities. Oocysts were recovered using continuous separation channel centrifugation and counted on membrane filters using epifluorescent microscopy. Recovery efficiencies of both parasites were > or =84% in 10 l volumes of drinking water. In source waters, recoveries ranged from 64% to 100%, with the lowest recoveries in the most turbid waters. Method precision was between 10% and 20% coefficient of variation. CONCLUSION: Toxoplasma gondii and C. cayetanensis are effectively concentrated from various water matrices by continuous separation channel centrifugation. SIGNIFICANCE AND IMPACT OF THE STUDY: Waterborne transmission of T. gondii and C. cayetanensis presents another challenge in producing clean drinking water and protecting public health. Detection of these parasites relies on effectively concentrating oocysts from ambient water, otherwise false negatives may result. Validation data specific to T. gondii and C. cayetanensis concentration methods are limited. Continuous separation channel centrifugation recovers oocysts with high efficiency and precision, the method attributes required to accurately assess the risk of waterborne transmission.

Concentration of Cryptosporidium, microsporidia and other water-borne pathogens by continuous separation channel centrifugation.

AIMS: The aim of this study was to determine the effectiveness of continuous separation channel centrifugation for concentrating water-borne pathogens of various taxa and sizes. METHODS AND RESULTS: Cryptosporidium parvum oocysts, Giardia lamblia cysts, Encephalitozoon intestinalis spores and Escherichia coli were seeded into different water matrices at densities ranging from 5 to 10 000 organisms l(-1) and recovered using continuous separation channel centrifugation. All pathogens were enumerated on membrane filters using microscopy. Recovery efficiencies were usually > 90%. Oocyst recovery did not vary with source water turbidity or with centrifuge flow rate up to 250 ml min(-1). Based on excystation, this concentration method did not alter oocyst viability. CONCLUSIONS: Continuous separation channel centrifugation is an effective means of concentrating water-borne pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: Methods are needed for detecting pathogens in drinking water to ensure public health. The first step for any pathogen detection procedure is concentration. However, this step has been problematic because recovery efficiencies of conventional methods, like filtration, are often low and variable, which may lead to false negatives. Continuous separation channel centrifugation can simultaneously concentrate multiple pathogens as small as 1 microm with high and reproducible efficiency in a variety of water matrices.

Non-melanoma skin cancers and glucocorticoid therapy.

Non-melanoma skin cancer (NMSC) is an important cause of morbidity and long-term mortality in organ transplant recipients receiving immunosuppressive drugs such as azathioprine and cyclosporin, often combined with adrenocortical steroids (glucocorticoids). At lower doses, glucocorticoids alone are prescribed for other conditions including musculoskeletal, connective tissue and respiratory disorders. Presently, it is unknown whether patients taking glucocorticoids are at an increased risk of skin malignancies. In a population-based case-control study in New Hampshire, USA, we compared use of glucocorticoids in 592 basal cell carcinoma (BCC) and 281 squamous cell carcinoma (SCC) cases and in 532 age and gender matched controls; neither cases nor controls had a history of organ transplantation. Participants underwent a structured personal interview regarding history of medication use and skin cancer risk factors. We used unconditional logistic regression analysis to compute odds ratios associated with glucocorticoid use for 1 month or longer while controlling for potential confounding factors. Risk of SCC was increased among users of oral glucocorticoids (adjusted odds ratio = 2.31; 95% CI = 1.27, 4.18), and risk of BCC was elevated modestly (adjusted odds ratio = 1.49; 95% CI = 0.90, 2.47). In contrast, risk of both SCC and BCC were unrelated to use of inhaled steroids. Our data suggest that use of oral glucocorticoids may increase risk of NMSC, and SCC in particular, among patients other than organ transplant recipients. We hypothesize that immunosuppression induced by oral glucocorticoids may allow these cancers to emerge from immunosurveillance.

Skin cancer risk in relation to toenail arsenic concentrations in a US population-based case-control study.

Arsenic is a known carcinogen specifically linked to skin cancer occurrence in regions with highly contaminated drinking water or in individuals who took arsenic-containing medicines. Presently, it is unknown whether such effects occur at environmental levels found in the United States. To address this question, the authors used data collected on 587 basal cell and 284 squamous cell skin cancer cases and 524 controls interviewed as part of a case-control study conducted in New Hampshire between 1993 and 1996. Arsenic was determined in toenail clippings using instrumental neutron activation analysis. The odds ratios for squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) were close to unity in all but the highest category. Among individuals with toenail arsenic concentrations above the 97th percentile, the adjusted odds ratios were 2.07 (95% confidence interval (CI): 0.92, 4.66) for SCC and 1.44 (95% CI: 0.74, 2.81) for BCC, compared with those with concentrations at or below the median. While the risks of SCC and BCC did not appear elevated at the toenail arsenic concentrations detected in most study subjects, the authors cannot exclude the possibility of a dose-related increase at the highest levels of exposure experienced in the New Hampshire population.

Therapeutic ionizing radiation and the incidence of basal cell carcinoma and squamous cell carcinoma. The New Hampshire Skin Cancer Study Group.

OBJECTIVE: To estimate the relative risk of developing basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) after receiving therapeutic ionizing radiation. DESIGN: Population-based case-control study. SETTING: New Hampshire. PATIENTS: A total of 592 cases of BCC and 289 cases of SCC identified through a statewide surveillance system and 536 age- and sex-matched controls selected from population lists. MAIN OUTCOME MEASURES: Histologically confirmed BCC and invasive SCC diagnosed between July 1, 1993, through June 30, 1995, among New Hampshire residents. RESULTS: Information regarding radiotherapy and other factors was obtained through personal interviews. An attempt was made to review the radiation treatment records of subjects who reported a history of radiotherapy. Overall, an increased risk of both BCC and SCC was found in relation to therapeutic ionizing radiation. Elevated risks were confined to the site of radiation exposure (BCC odds ratio, 3. 30; 95% confidence interval, 1.60-6.81; SCC odds ratio, 2.94; 95% confidence interval, 1.30-6.67) and were most pronounced for those irradiated for acne exposure. For SCC, an association with radiotherapy was observed only among those whose skin was likely to sunburn with sun exposure. CONCLUSIONS: These results largely agree with those of previous studies on the risk of BCC in relation to ionizing radiation exposure. In addition, they suggest that the risk of SCC may be increased by radiotherapy, especially in individuals prone to sunburn with sun exposure. Arch Dermatol. 2000;136:1007-1011

Multi-drug resistance in chronic lymphocytic leukemia.

We evaluated 45 chronic lymphocyte leukemia (CLL) patients for the presence of multi-drug resistance (MDR) by the ex vivo techniques: 1) a functional assay utilizing doxorubicin (dox) retention with modulation; 2) a cytotoxicity assay (MTT) with modulation; 3) and four monoclonal antibodies. Ex vivo tests were correlated with disease stage and prior treatment, and were repeated as patients became resistant to alkylating agents, fludarabine and VAD chemotherapy (infusion of vincristine, dox, and oral dexamethasone). The majority of patients (64.4%) were in early stage and were untreated (62.2%). P-glycoprotein (p-gp 170) was detected most frequently by the monoclonal antibody MRK-16 (48%) and by functional modulation of dox retention by PSC-833 (40.6%) and by functional modulation of the MTT assay with vincristine (0.29) and dox (0.39) with PSC-833 at 1.0 microg/mL. Functional modulation of dox retention with PSC-833 was significantly associated with stage, but not with either the MTT assay or any of the monoclonal antibodies. None of the tests correlated with prior chlorambucil treatment. Correlation of dox retention with the monoclonal antibodies was mild to moderate and became stronger following chlorambucil treatment. Three patients who became resistant to VAD were found to express p-gp 170. We conclude that MDR can frequently be detected in patients with CLL. Furthermore, the expression of p-gp 170 increases with advancing stage, but not prior alkylating agent therapy. The functional expression of p-gp 170 increases with advancing stage and prior treatment and correlates well with monoclonal antibody detection (especially MRK-16). Patients who become resistant to VAD more frequently express p-gp 170 by a variety of techniques. PSC-833 is a more potent modulator of MDR than cyclosporin-A (CsA) ex vivo, and correlates better with stage of disease.

Parry-Romberg syndrome with contralateral and ipsilateral extremity involvement.

BACKGROUND: The Parry-Romberg syndrome is an acquired progressive hemifacial atrophy involving the subcutaneous tissues of the scalp and face. Involvement of the extremities is uncommon in this syndrome. OBJECTIVE: A case of contralateral and ipsilateral extremity involvement in the Parry-Romberg syndrome is reported, and the difficulties in distinguishing this syndrome from linear scleroderma en coup de sabre are reviewed. METHODS: A MEDLINE search for cases of Parry-Romberg syndrome with contralateral extremity involvement was performed and the cases reviewed. RESULTS: Contralateral extremity involvement in the Parry-Romberg syndrome is rare. CONCLUSION: This may be the first case reported in the English literature of Parry-Romberg syndrome with contralateral and ipsilateral extremity involvement.

Increase in incidence rates of basal cell and squamous cell skin cancer in New Hampshire, USA. New Hampshire Skin Cancer Study Group.

We conducted a study to estimate the current incidence rates of basal-cell carcinoma (BCC) and squamous-cell carcinoma (SCC) of the skin in the population of New Hampshire (NH), USA, and to quantify recent changes in the incidence rates of these malignancies. BCCs and SCCs diagnosed among NH residents were identified through physician practices and central pathology laboratories in NH and bordering regions from June 1979 through May 1980 and from July 1993 through June 1994. For each diagnosis period, we estimated the age-adjusted incidence rates for both BCC and SCC among both men and women and for separate anatomic sites. Between 1979-1980 and 1993-1994, incidence rates of SCC increased by 235% in men and by 350% in women. Incidence rates of BCC increased by more than 80% in both men and women. While the absolute increase was greatest for tumors of the head and neck, the relative change was most pronounced for tumors on the trunk in men and on the lower limb in women. Thus, there has been a marked rise in the incidence rates of BCC and SCC skin cancers in NH in recent years. The anatomic pattern of increase in BCC and SCC incidence is consistent with an effect of greater sunlight exposure. Studies of BCC and SCC occurrence are needed to identify possible behavioral and environmental factors and to assess possible changes in diagnostic practices that might account for the rise in incidence of these common malignancies.

Severely atypical medium-sized congenital nevus with widespread satellitosis and placental deposits in a neonate: the problem of congenital melanoma and its simulants.

We describe a neonate with a highly atypical melanocytic proliferation that arose in a medium-sized congenital nevus, in association with multiple cutaneous satellite lesions and placental deposits. The patient's pathologic findings and benign clinical course to date raise the problem of diagnosis of congenital melanoma and the importance of clinical follow-up to determine the biologic behavior of severely atypical, histologically malignant proliferations in congenital melanocytic nevi.

A clinical trial of beta carotene to prevent basal-cell and squamous-cell cancers of the skin. The Skin Cancer Prevention Study Group.

BACKGROUND: Beta carotene has been associated with a decreased risk of human cancer in many studies employing dietary questionnaires or blood measurements, and it has had protective effects in some animal models of carcinogenesis. METHODS: We tested the possible cancer-preventing effects of beta carotene by randomly assigning 1805 patients who had had a recent nonmelanoma skin cancer to receive either 50 mg of beta carotene or placebo per day and by conducting annual skin examinations to determine the occurrence of new nonmelanoma skin cancer. RESULTS: Adherence to the prescribed treatment was good, and after one year the actively treated group's median plasma beta carotene level (3021 nmol per liter) was much higher than that of the control group (354 nmol per liter). After five years of follow-up, however, there was no difference between the groups in the rate of occurrence of the first new nonmelanoma skin cancer (relative rate, 1.05; 95 percent confidence interval, 0.91 to 1.22). In subgroup analyses, active treatment showed no efficacy either in the patients whose initial plasma beta carotene level was in the lowest quartile or in those who currently smoked. There was also no significant difference between treated and control groups in the mean number of new nonmelanoma skin cancers per patient-year. CONCLUSIONS: In persons with a previous nonmelanoma skin cancer, treatment with beta carotene does not reduce the occurrence of new skin cancers over a five-year period of treatment and observation.