Evidence of a healthy volunteer effect in the prostate, lung, colorectal, and ovarian cancer screening trial

Volunteers for prevention or screening trials are generally healthier and have lower mortality than the general population. The Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) is an ongoing, multicenter, randomized trial that randomized 155,000 men and women aged 55-74 years to a screening or control arm between 1993 and 2001. The authors compared demographics, mortality rates, and cancer incidence and survival rates of PLCO subjects during the early phase of the trial with those of the US population. Incidence and mortality from PLCO cancers (prostate, lung, colorectal, and ovarian) were excluded because they are the subject of the ongoing trial. Standardized mortality ratios for all-cause mortality were 46 for men, 38 for women, and 43 overall (100 = standard). Cause-specific standardized mortality ratios were 56 for cancer, 37 for cardiovascular disease, and 34 for both respiratory and digestive diseases. Standardized mortality ratios for all-cause mortality increased with time on study from 31 at year 1 to 48 at year 7. Adjusting the PLCO population to a standardized demographic distribution would increase the standardized mortality ratio only modestly to 54 for women and 55 for men. Standardized incidence ratios for all cancer were 84 in women and 73 in men, with a large range of standardized incidence ratios observed for specific cancers.

Risk behaviours and benign prostatic hyperplasia

OBJECTIVE

To identify risk factors for benign prostatic hyperplasia (BPH).

SUBJECTS AND METHODS

Medical history data, including reported urological conditions and treatments, and risk factor data were collected from 34 694 participants in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, a randomized controlled trial designed to evaluate methods for the early detection of cancer.

RESULTS

Asian men had the lowest risks (odds ratio, 95% confidence interval) for nocturia (0.7, 0.5-0.9), physician-diagnosed BPH (0.3, 0.2-0.5) and transurethral prostatectomy (TURP, 0.2, 0.1-0.6), while risks for Whites and Blacks were similar for most measures of BPH. Greater alcohol intake was associated with decreased nocturia (P trend = 0.002), BPH (P trend < 0.001) and TURP (P trend < 0.001). Current tobacco use was associated with decreased nocturia (0.8, 0.7-0.9), BPH (0.7, 0.6-0.8) and TURP (0.6, 0.4-0.8) but dose-response patterns were weak.

CONCLUSION

Asian-Americans have the lowest risk of clinical BPH. Alcohol and possibly cigarettes are related to a lower risk for BPH.

Relationship of demographic and clinical factors to free and total prostate-specific antigen

OBJECTIVES

To characterize the role of demographic and clinical parameters in the measurements of prostate-specific antigen (PSA), free PSA (fPSA), and percent free PSA (%fPSA).

METHODS

This was a cohort study of volunteers to a randomized screening trial. A central laboratory determined PSA and fPSA for the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. A baseline evaluation of free and total PSA was done for 7183 white, black, Asian, Hispanic, and other male volunteers, aged 55 to 74 years. Comparisons were made across racial and ethnic groups and across a set of clinical parameters from a baseline questionnaire.

RESULTS

The median levels of serum PSA were less than 2.1 ng/mL in each age-race grouping of the study participants. The levels of free and total PSA were higher in black (n = 868, 12%) participants than in white (n = 4995, 70%) and Asian (n = 849, 11.8%) participants. Individuals who identified themselves as ethnically Hispanic (n = 339, 4.7%) had median PSA levels higher than whites who were not Hispanic. The free and total PSA levels increased with age, particularly among men 70 to 74 years old. However, the %fPSA levels showed less variation among the four racial groups or by age. The free and total PSA levels were higher among those who had a history of benign prostatic disease.

CONCLUSIONS

Demographic (age and race/ethnicity) and clinical (history of benign prostatic disease) variables had a moderate effect on the measures of PSA and fPSA and very little effect on %fPSA.

Is shorter always better? Relative importance of questionnaire length and cognitive ease on response rates and data quality for two dietary questionnaires

In this study, the authors sought to determine the effects of length and clarity on response rates and data quality for two food frequency questionnaires (FFQs): the newly developed 36-page Diet History Questionnaire (DHQ), designed to be cognitively easier for respondents, and a 16-page FFQ developed earlier for the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. The PLCO Trial is a 23-year randomized controlled clinical trial begun in 1992. The sample for this substudy, which was conducted from January to April of 1998, consisted of 900 control and 450 screened PLCO participants aged 55-74 years. Controls received either the DHQ or the PLCO FFQ by mail. Screenees, who had previously completed the PLCO FFQ at baseline, were administered the DHQ. Among controls, the response rate for both FFQs was 82%. Average amounts of time needed by controls to complete the DHQ and the PLCO FFQ were 68 minutes and 39 minutes, respectively. Percentages of missing or uninterpretable responses were similar between instruments for questions on frequency of intake but were approximately 3 and 9 percentage points lower (p < or = 0.001) in the DHQ for questions on portion size and use of vitamin/mineral supplements, respectively. Among screenees, response rates for the DHQ and the PLCO FFQ were 84% and 89%, respectively, and analyses of questions on portion size and supplement use showed few differences. These data indicated that the shorter FFQ was not better from the perspective of response rate and data quality, and that clarity and ease of administration may compensate for questionnaire length.

Etiologic and early marker studies in the prostate, lung, colorectal and ovarian (PLCO) cancer screening trial

The Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial, which is randomizing 74,000 screening arm participants (37,000 men, 37,000 women; ages 55-74) and an equal number of nonscreened controls, is a unique setting for the investigation of the etiology of cancer and other diseases and for the evaluation of potential molecular markers of early disease. At entry, baseline information is collected by questionnaire on dietary intake, tobacco and alcohol use, reproductive history (for women), family history of cancer, use of selected drugs, and other selected risk factors. Blood samples collected at the baseline screening exam are aliquoted to serum, plasma, red blood cell, and buffy coat fractions. At the next two annual screening visits, serum samples are collected. At the third annual reexamination, cryopreserved whole blood is obtained, in addition to serum, plasma, red blood cell, and buffy coat fractions. At the fourth and fifth years, serum, plasma, and buffy coat are collected. All blood samples are shipped to a central repository for long-term storage at -70 degrees C. Dietary questionnaires and buccal cells for DNA analysis are obtained from nonscreened controls. Cancer cases are identified through annual follow-up questionnaires, and all deaths are identified through vital status tracing mechanisms. Procedures are being developed to obtain archival pathologic material for selected cases of cancer and related diseases. Initial investigations are focusing on the etiology of colorectal cancer and on the operative characteristics of tests for the early detection of colorectal and prostate cancer.

Design of the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial

The objectives of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial are to determine in screenees ages 55-74 at entry whether screening with flexible sigmoidoscopy (60-cm sigmoidoscope) can reduce mortality from colorectal cancer, whether screening with chest X-ray can reduce mortality from lung cancer, whether screening men with digital rectal examination (DRE) plus serum prostate-specific antigen (PSA) can reduce mortality from prostate cancer, and whether screening women with CA125 and transvaginal ultrasound (TVU) can reduce mortality from ovarian cancer. Secondary objectives are to assess screening variables other than mortality for each of the interventions including sensitivity, specificity, and positive predictive value; to assess incidence, stage, and survival of cancer cases; and to investigate biologic and/or prognostic characterizations of tumor tissue and biochemical products as intermediate endpoints. The design is a multicenter, two-armed, randomized trial with 37,000 females and 37,000 males in each of the two arms. In the intervention arm, the PSA and CA125 tests are performed at entry, then annually for 5 years. The DRE, TVU, and chest X-ray exams are performed at entry and then annually for 3 years. Sigmoidoscopy is performed at entry and then at the 5-year point. Participants in the control arm follow their usual medical care practices. Participants will be followed for at least 13 years from randomization to ascertain all cancers of the prostate, lung, colorectum, and ovary, as well as deaths from all causes. A pilot phase was undertaken to assess the randomization, screening, and data collection procedures of the trial and to estimate design parameters such as compliance and contamination levels. This paper describes eligibility, consent, and other design features of the trial, randomization and screening procedures, and an outline of the follow-up procedures. Sample-size calculations are reported, and a data analysis plan is presented.

Complex ovarian cysts in postmenopausal women are not associated with ovarian cancer risk factors: preliminary data from the prostate, lung, colon, and ovarian cancer screening trial

OBJECTIVE

We assessed whether asymptomatic ovarian abnormalities detected on ultrasonography in postmenopausal women are precursors to ovarian cancer.

STUDY DESIGN

We compared the transvaginal ultrasonographic findings from the initial examination of 20,000 postmenopausal women enrolled to date in an ongoing randomized trial of cancer screening with data on the established risk factors for ovarian cancer obtained from self-administered questionnaires. We distinguished cysts with the suggestive characteristic(s) of a septum, a solid component, or an irregular or thick wall ("complex cysts") from simple sonolucent cysts with none of those features.

RESULTS

High parity, a strong ovarian cancer protective factor, was negatively associated with complex cysts (odds ratio for > or =5 births vs no births, 0.72; 95% confidence interval, 0.53-0.97), but long-term oral contraceptive use, another strong ovarian cancer protective factor, was not associated with complex cysts (odds ratio, 0.96; 95% confidence interval, 0.76-1.20). A family history of ovarian cancer or multiple breast cancers, a strong risk factor for cancer, was not associated with complex cysts (odds ratio, 0.99; 95% confidence interval, 0.68-1.44). Other abnormalities found on ultrasonography (including simple cysts, bilateral cysts, or all abnormalities combined) also did not share the established risk factors for ovarian malignancy. We did not identify any combination of features of abnormalities (septum, echogenicity, size, or papillary projections) that manifested the cancer risk factor profile.

CONCLUSIONS

Although a very small proportion of the clinically silent ovarian abnormalities found on ultrasonography are determined to be ovarian cancers, the remaining complex cysts and other clinically suspicious abnormalities do not appear to be the immediate precursors of ovarian cancer. The eventual identification of such precursors will yield opportunities for earlier diagnosis, screening of high-risk groups, and better understanding of the cause of this often lethal malignancy.

Complex ovarian cysts in postmenopausal women are not associated with ovarian cancer risk factors. Preliminary data from the plco cancer screening trial

PURPOSE: We assessed whether ovarian abnormalities detected on ultrasound in postmenopausal women are precursors to ovarian cancer.METHODS: We compared the transvaginal ultrasound findings from the initial examination of twenty thousand postmenopausal women enrolled to date in an ongoing randomized trial of cancer screening to data on the established risk factors for ovarian cancer obtained from self-administered questionnaires. We distinguished cysts with the suspicious characteristics of a septum, solid component, irregular or thick wall ("complex cysts") from simple sonolucent cysts with none of those features.RESULTS: High parity, protective for cancer, was negatively associated with complex cysts (Odds Ratio ["OR"] for five or more births versus no births = 0.72, 95% CI = 0.53-0.97), but long-term oral contraceptive use was not (OR = 0.96, 95% CI = 0.76-1.20). A family history of ovarian cancer or multiple breast cancers, a strong risk factor for cancer, was not associated with complex cysts (OR = 0.99, 95% CI = 0.68-1.44). Other abnormalities found on ultrasound (including simple cysts, bilateral cysts, or all abnormalities combined) also did not share the established risk factors for ovarian malignancy. We formed no combination of features of abnormalities (septum, echogenicity, size, or papillary projection) with the cancer risk factor profile.CONCLUSIONS: Although a very small proportion of the clinically silent ovarian abnormalities found on ultrasound are found to be ovarian cancers, the remaining complex cysts and other clinically suspicious abnormalities do not appear to be the immediate precursors of ovarian cancer.

Wisconsin farmer cancer mortality, 1981 to 1990: selected malignancies

Cancer mortality risks for Wisconsin white male farmers were examined during the years 1981 to 1990. Four malignancies were studied: Non-Hodgkin's lymphoma, melanoma, colon cancer, and rectal cancer. Occupation coded deaths were segmented into farmer and nonfarmer groups and population counts for the groups were estimated from 1980 and 1990 Bureau of the Census data. Standardized mortality ratios (SMRs) were constructed from the ratio of observed farmer deaths and the expected number of farmer deaths. Expected deaths were generated from the underlying statewide nonfarmer rate for the malignancy multiplied into the farmer population at risk. Farmers had significantly lower mortality risks for melanoma (SMR: 0.659; 95% CI: 0.993-0.326) and colon cancer (SMR: 0.763; 95% CI: 0.928-0.599). Farmers also exhibited a nonsignificant decrement for non-Hodgkin's lymphoma (SMR: 0.930; 95% CI: 1.214-0.645). For rectal cancer, farmers experienced a slightly higher but essentially the same risk as nonfarmers (SMR: 1.013; 95% CI: 1.418-0.608)--the SMR was not significant. This study corroborates a number of cancer incidence and mortality investigations demonstrating that farmers generally experience the same or lower mortality risks for these malignancies.

Outcomes, preferences for resuscitation, and physician-patient communication among patients with metastatic colorectal cancer. SUPPORT Investigators. Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments

PURPOSE

To describe characteristics, outcomes, and decision making in patients with colorectal cancer metastatic to the liver, and to examine the relationship of doctor-patient communication with patient understanding of prognosis and physician understanding of patients' treatment preferences.

PATIENTS AND METHODS

The Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT) was a prospective cohort study conducted at five teaching hospitals in the United States between 1989 and 1994. Participants in this study were hospitalized patients 18 years of age or older with known liver metastases who had been diagnosed with colorectal cancer at least 1 month earlier. Data were collected by patient interview and chart review at study entry; patients were interviewed again at 2 and 6 months. Data collected by physician interview included estimates of survival and impressions of patients' preferences for cardiopulmonary resuscitation (CPR). Patients and physicians were also asked about discussions about prognosis and resuscitation preferences.

RESULTS

We studied 520 patients with metastatic colorectal cancer (median age 64, 56% male, 80% white, 2-month survival 78%, 6-month survival 56%). Quality of life (62% "good" to "excellent") and functional status (median number of disabilities = 0) were high at study entry and remained so among interviewed survivors at 2 and 6 months. Of 339 patients with available information, 212 (63%) of 339 wanted CPR in the event of a cardiopulmonary arrest. Factors independently associated with preference for resuscitation included younger age, better quality of life, absence of lung metastases, and greater patient estimate of 2-month prognosis. Of the patients who preferred not to receive CPR, less than half had a do-not-resuscitate note or order written. Patients' self-assessed prognoses were less accurate than those of their physicians. Physicians incorrectly identified patient CPR preferences in 30% of cases. Neither patient prognostication nor physician understanding of preferences were significantly better when discussions were reported between doctors and patients.

CONCLUSIONS

A majority of patients with colorectal cancer have preferences regarding end of life care. The substantial misunderstanding between patients and their physicians about prognosis and treatment preferences appears not to be improved by direct communication. Future research focused on enhancing the effectiveness of communication between patients and physicians about end of life issues is needed.

Relationship between cancer patients' predictions of prognosis and their treatment preferences

CONTEXT

Previous studies have documented that cancer patients tend to overestimate the probability of long-term survival. If patient preferences about the trade-offs between the risks and benefits associated with alternative treatment strategies are based on inaccurate perceptions of prognosis, then treatment choices may not reflect each patient's true values.

OBJECTIVE

To test the hypothesis that among terminally ill cancer patients an accurate understanding of prognosis is associated with a preference for therapy that focuses on comfort over attempts at life extension.

DESIGN

Prospective cohort study.

SETTING

Five teaching hospitals in the United States.

PATIENTS

A total of 917 adults hospitalized with stage III or IV non-small cell lung cancer or colon cancer metastatic to liver in phases 1 and 2 of the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT).

MAIN OUTCOME MEASURES

Proportion of patients favoring life-extending therapy over therapy focusing on relief of pain and discomfort, patient and physician estimates of the probability of 6-month survival, and actual 6-month survival.

RESULTS

Patients who thought they were going to live for at least 6 months were more likely (odds ratio [OR], 2.6; 95% confidence interval [CI], 1.8-3.7) to favor life-extending therapy over comfort care compared with patients who thought there was at least a 10% chance that they would not live 6 months. This OR was highest (8.5; 95% CI, 3.0-24.0) among patients who estimated their 6-month survival probability at greater than 90% but whose physicians estimated it at 10% or less. Patients overestimated their chances of surviving 6 months, while physicians estimated prognosis quite accurately. Patients who preferred life-extending therapy were more likely to undergo aggressive treatment, but controlling for known prognostic factors, their 6-month survival was no better.

CONCLUSIONS

Patients with metastatic colon and lung cancer overestimate their survival probabilities and these estimates may influence their preferences about medical therapies.

Is economic hardship on the families of the seriously ill associated with patient and surrogate care preferences? SUPPORT Investigators

BACKGROUND

Serious illness often causes economic hardship for patients' families. However, it is not known whether this hardship is associated with a preference for the goal of care to focus on maximizing comfort instead of maximizing life expectancy or whether economic hardship might give rise to disagreement between patients and surrogates over the goal of care.

METHODS

We performed a cross-sectional study of 3158 seriously ill patients (median age, 63 years; 44% women) at 5 tertiary medical centers with 1 of 9 diagnoses associated with a high risk of mortality. Two months after their index hospitalization, patients and surrogates were surveyed about patients' preferences for the primary goal of care: either care focused on extending life or care focused on maximizing comfort. Patients and surrogates were also surveyed about the financial impact of the illness on the patient's family.

RESULTS

A report of economic hardship on the family as a result of the illness was associated with a preference for comfort care over life-extending care (odds ratio, 1.26; 95% confidence interval, 1.07-1.48) in an age-stratified bivariate analysis. Similarly, in a multivariable analysis controlling for patient demographics, illness severity, functional dependency, depression, anxiety, and pain, economic hardship on the family remained associated with a preference for comfort care over life-extending care (odds ratio, 1.31; 95% confidence interval, 1.10-1.57). Economic hardship on the family did not affect either the frequency or direction of patient-surrogate disagreements about the goal of care.

CONCLUSIONS

In patients with serious illness, economic hardship on the family is associated with preferences for comfort care over life-extending care. However, economic hardship on the family does not appear to be a factor in patient-surrogate disagreements about the goal of care.

Generalizability of clinical studies conducted at tertiary care medical centers: a population-based analysis

The Marshfield Epidemiologic Study Area (MESA), a geographically defined population registry at one of the participating sites in SUPPORT (a multicenter study of the care of seriously ill hospitalized patients) permitted assessment of generalizability in that study. On the basis of age- and sex-specific rates of enrollment of SUPPORT patients in MESA, we estimate that about 400,000 patients per year would fulfill SUPPORT eligibility criteria in the United States. However, an estimated 925,000 patients, particularly the elderly and those with impairments in their activities of daily living (ADLs), have SUPPORT-like illnesses annually, but do not receive the aggressive care required for study enrollment. The absence of patients not interested in aggressive care in tertiary care-based studies is compounded by the overrepresentation of patients referred from distant areas to the tertiary care center. Such patients tended to be older and to have different diseases than patients in MESA. Care should be taken in generalizing results from clinical and epidemiologic studies conducted at tertiary care centers.

Surrogates' predictions of seriously ill patients' resuscitation preferences

BACKGROUND

Seriously or terminally ill patients are frequently incapacitated and unable to express their preferences regarding cardiopulmonary resuscitation (CPR). In this situation, family members or other surrogate decision makers are often asked whether they believe the patient would want to be resuscitated. We evaluated the concordance of patient CPR preferences and surrogate perceptions of the patient preferences in the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT), a large, multicenter study of seriously ill hospitalized patients.

METHODS

We compared patient preferences and surrogate perceptions in 1226 pairings in which both patient and surrogate responded to CPR decision questions. We also examined factors that might influence patient-surrogate concordance.

RESULTS

Twenty-nine percent of patients with paired data did not want to be resuscitated; 26% of surrogates did not believe the patient they represented would want to be resuscitated. Within pairs, the overall exact agreement with respect to CPR decisions was 74%. For patients favoring CPR, only 16% of the surrogates misconstrued the patient's wishes. For patients who did not want to be resuscitated, however, 50% of the surrogates did not reflect the patient's wishes. If patients reported telling surrogates their CPR preference, concordance was significantly improved if the surrogate believed the patient did not want to be resuscitated and was significantly worsened if the surrogate believed the patient wanted CPR. This finding is likely an artifact of patients being more likely to report their preference to surrogates if that preference was not to be resuscitated.

CONCLUSIONS

Surrogates' perceptions of patient CPR preferences are often inaccurate, particularly for those patients who do not want to be resuscitated. Methods to improve communication between patients and surrogates on CPR preferences should be developed and evaluated.

The impact of serious illness on patients' families. SUPPORT Investigators. Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatment

OBJECTIVE

To examine the impact of illness on the families of seriously ill adults and to determine the correlates of adverse economic impact.

DESIGN

Data were collected during the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatment (SUPPORT), a prospective cohort study of outcomes, preferences, and decision making in seriously ill hospitalized adults and their families.

SETTING

Five tertiary care hospitals in the United States.

PARTICIPANTS

The 2661 seriously ill patients in nine diagnostic categories who survived their index hospitalization and were discharged home were eligible for this analysis. Surrogate and/or patient interviews about the impact of illness on the family were obtained for 2129 (80%) of these patients (mean age, 62 years; 43% women; 6-month survival, 75%).

OUTCOME MEASURES

Surrogates and patients were surveyed to determine the frequency of adverse caregiving and economic burdens. Multivariable analyses were performed to determine correlates of loss of family savings.

RESULTS

One third (34%) of patients required considerable caregiving assistance from a family member. In 20% of cases, a family member had to quit work or make another major life change to provide care for the patient. Loss of most or all of the family savings was reported by 31% of families, whereas 29% reported loss of the major source of income. Patient factors independently associated with loss of the family's savings on multivariable analysis included poor functional status (odds ratio [OR], 1.40; 95% confidence interval [CI], 1.10 to 1.78 for patients needing assistance with three or more activities of daily living), lower family income (OR, 1.74; 95% CI, 1.37 to 2.21 for those with annual incomes below $25,000), and young age (OR, 2.85; 95% CI, 2.13 to 3.82 for those younger than 45 years compared with those 65 years or older).

CONCLUSIONS

Many families of seriously ill patients experience severe caregiving and financial burdens. Families of younger, poorer, and more functionally dependent patients are most likely to report loss of most or all of the family's savings.

Peer discussions of cancer among Hispanic migrant farm workers

Hispanic migrant agricultural workers' exposure to pesticides and other agrichemicals places them at increased risk for a variety of acute and chronic conditions, including cancer. As a socioeconomically disadvantaged group, migrant workers also face many barriers to effective cancer control. In 1992, a series of focus groups was held with 55 Hispanic migrant agricultural workers (22 women, 33 men) in central Wisconsin to gather information on their knowledge and attitudes regarding cancer etiology and treatment, their practices regarding cancer screening and early detection, and their concerns regarding occupational exposure to pesticides. Beliefs that pesticides are toxic and can cause health problems were common among participants. In addition, however, participants reported that they are reluctant to demand occupational protections to which they are entitled because they are afraid of losing their jobs. Study results also suggest that barriers to effective primary and secondary prevention of cancer in this Hispanic migrant agricultural worker population include knowledge and information barriers, cultural barriers, and socioeconomic barriers. A lack of knowledge and information regarding the causes of cancer, its prevention, and its early detection and treatment was evident among participants, which in turn was reflected in strong fatalistic attitudes toward the disease. Cultural barriers included attitudes of embarrassment and shame associated with physical examinations and women's strong discomfort with male clinicians. Socioeconomic barriers to secondary prevention included the cost of obtaining health services, time constraints associated with the need to work and long working days, and a lack of transportation. Efforts to improve cancer screening as well as other preventive health services in the Hispanic migrant agricultural worker population must acknowledge these barriers and address as many of them as possible to be successful.

Phase I trial of an oral immunomodulator and interferon inducer in cancer patients

Imiquimod [1-(2-methylpropyl)-1H-imidazo[4,5c]quinolin-4-amine] is a compound of low molecular weight that, when administered p.o., induces interferon-alpha in several animal species and inhibits tumor growth in mice. To determine maximum tolerated dose, toxicity, and biological response in humans, a phase I clinical trial was conducted with 14 eligible cancer patients who received 100-500 mg imiquimod p.o. either once or twice weekly. Imiquimod induced interferon-alpha in serum in 10 of 19 doses of 200-300 mg. Interferon serum levels peaked 8-24 h after treatment and reached a maximum of 23,000 IU/ml in one patient. Significant mean increases (P < 0.01) in serum beta 2-microglobulin (1.5-fold), serum neopterin (3.5-fold), and 2-5A synthetase activity in peripheral blood mononuclear cells (7.9-fold) indicated that 200-300 mg imiquimod had biological and immunological activity in all evaluable patients. Increases in serum interferon, beta 2-microglobulin, and neopterin correlated significantly with dose (P < 0.001). No patient developed measurable antibody to interferon-alpha. Dose-limiting side effects included fatigue, malaise, fever, headache, and lymphocytopenia; no hepatic or renal toxicity or other hematological changes exceeded the normal range. Patients tolerated weekly doses of up to 500 mg, with the longest treatment lasting 4 weeks at 200 mg weekly. Twice-weekly doses up to to 300 mg were tolerated, with the longest twice-weekly treatments being 200 mg for 9 weeks and 100 mg for 25 weeks. No clinical responses were observed. Imiquimod, as an oral inducer of interferon, may have therapeutic usefulness in human cancers, viral infections, and other diseases. However, before initiation of phase II trials, additional work will be required to establish a tolerated dose and schedule for continued administration.