Estimates of benefits and harms of prophylactic use of aspirin in the general population.

BACKGROUND: Accumulating evidence supports an effect of aspirin in reducing overall cancer incidence and mortality in the general population. We reviewed current data and assessed the benefits and harms of prophylactic use of aspirin in the general population. METHODS: The effect of aspirin for site-specific cancer incidence and mortality, cardiovascular events was collated from the most recent systematic reviews. Studies identified through systematic Medline search provided data regarding harmful effects of aspirin and baseline rates of harms like gastrointestinal bleeding and peptic ulcer. RESULTS: The effects of aspirin on cancer are not apparent until at least 3 years after the start of use, and some benefits are sustained for several years after cessation in long-term users. No differences between low and standard doses of aspirin are observed, but there were no direct comparisons. Higher doses do not appear to confer additional benefit but increase toxicities. Excess bleeding is the most important harm associated with aspirin use, and its risk and fatality rate increases with age. For average-risk individuals aged 50-65 years taking aspirin for 10 years, there would be a relative reduction of between 7% (women) and 9% (men) in the number of cancer, myocardial infarction or stroke events over a 15-year period and an overall 4% relative reduction in all deaths over a 20-year period. CONCLUSIONS: Prophylactic aspirin use for a minimum of 5 years at doses between 75 and 325 mg/day appears to have favourable benefit-harm profile; longer use is likely to have greater benefits. Further research is needed to determine the optimum dose and duration of use, to identify individuals at increased risk of bleeding, and to test effectiveness of Helicobacter pylori screening-eradication before starting aspirin prophylaxis.

From adjuvant therapy to breast cancer prevention: BCPT and STAR.

The continued widespread prevalence of breast cancer supports placing a high priority on research aimed at its primary prevention, particularly among women who are at increased risk for developing this disease. The suggestion of potential agents for the primary chemoprevention of breast cancer evolved out of the treatment setting. Extensive experience with tamoxifen, a first-generation selective estrogen receptor modulator (SERM) showing efficacy, first, in the treatment of advanced breast cancer and, subsequently, as adjuvant therapy for early stage disease established the safety of this agent. Cumulative data from multiple adjuvant studies documented the efficacy of tamoxifen in reducing second primary breast cancers in the contralateral breast, supporting its potential as a chemopreventive agent for breast cancer. The safety and second primary data on tamoxifen, together with extensive information on its pharmacokinetics, metabolism, and antitumor effects, as well as its potentially beneficial effects on lipid metabolism and osteoporosis, led the National Surgical Adjuvant Breast and Bowel Project (NSABP) to select tamoxifen for testing in the first prospective randomized phase III trial of the efficacy of a chemopreventive agent for preventing breast cancer in women at increased risk of the disease. Accordingly, in 1992 the NSABP started the Breast Cancer Prevention Trial (P-1) in which 13,388 women > or = 35 years of age who were at increased risk of breast cancer according to Gail model risk factors [family history, age, and personal history (i.e., age at first birth, age at menarche, previous breast biopsies)] were randomized to tamoxifen 20 mg/day or placebo for 5 years. Through 69 months of follow-up tamoxifen reduced the risk of invasive breast cancer, primarily estrogen receptor-positive tumors, by 49% (two-sided p < 0.00001). Tamoxifen reduced the risk of noninvasive breast cancer by 50% (two-sided p < 0.002). In addition, tamoxifen reduced fractures of the hip, radius, and spine, but it had no effect on the rate of ischemic heart disease. As previously shown, the rates of endometrial cancer and vascular events increased with tamoxifen. With the P-1 results establishing tamoxifen as the standard of care for the primary chemoprevention of breast cancer in high-risk women, concern over the side effects of tamoxifen has prompted a continuing search for an agent that displays a more desirable efficacy/toxicity profile. Raloxifene, a second-generation SERM approved for the prevention of osteoporosis in postmenopausal women, displays antiestrogenic properties in the breast and possibly the endometrium, and estrogenic effects in the bone and on the lipid profile, suggesting it as a candidate for comparison with the chemopreventive standard, tamoxifen. Raloxifene will be compared to tamoxifen in an equivalency trial, the Study of Tamoxifen and Raloxifene (STAR) NSABP P-2, which began in July 1999 at almost 500 centers in North America. The plan is to randomize 22,000 postmenopausal women > or = 35 years of age at increased risk of breast cancer by Gail criteria to tamoxifen 20 mg/day or raloxifene 60 mg/day for 5 years. Study endpoints include invasive and noninvasive breast cancer, cardiovascular disease, endometrial cancer, bone fractures, and vascular events.

Phase III, large-scale chemoprevention trials. Approach to chemoprevention clinical trials and phase III clinical trial of tamoxifen as a chemopreventive for breast cancer--the US National Cancer Institute experience.

Clinical trials to evaluate interventions for cancer prevention are designed as early (phase I, IIa, and IIb) or late-phase studies. Whereas the former are small and generally rely on intermediate endpoint biomarkers of carcinogenesis, the latter are large-scale, long-term, randomized, phase III studies that address endpoints such as cancer incidence. The Breast Cancer Prevention Trial, P-1, conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP), is discussed as an example of a large, extended, phase III trial designed to answer the question of whether tamoxifen reduces the incidence of breast cancer in women who are at increased risk for the disease.

Design of the Prostate Cancer Prevention Trial (PCPT).

The PCPT is a chemoprevention trial of finasteride with a primary endpoint of biopsy-proven presence or absence of prostate cancer. A total of 18,000 healthy men, aged 55 years and older, will be randomized. Half will receive finasteride (5 mg/day) and half will receive placebo (one matching tablet per day) for 7 years. The trial is designed to have 92% power to detect a 25% reduction in period prevalence of biopsy-proven disease using a two-sided test with alpha = 0.05. The trial is complicated by the known impact of finasteride on the major screening test for prostate cancer, prostate specific antigen (PSA). This paper describes the PCPT design with reference to alternatives that were considered. The chosen design depends on five critical assumptions that must be monitored closely throughout the 9-year trial.

The potential for hormonal prevention trials.

Breast and prostate cancer are significant causes of morbidity and mortality and are very similar in etiology, epidemiology, and modalities of treatment. Investigational strategies in the prevention of these malignancies also have strong parallels. The National Cancer Institute is sponsoring several large scale clinical trials involving hormonal manipulation and cancer prevention. In the Breast Cancer Prevention Trial, 16,000 women at high risk for breast cancer are being randomized to receive the antiestrogen agent tamoxifen or placebo for 5 years in an effort to determine if breast cancer development can be inhibited. In a similar trial, the Prostate Cancer Prevention Trial, 18,000 men older than 55 years of age will be randomized to receive finasteride, a 5-alpha-reductase inhibitor, or placebo to determine if inhibition of dihydrotestosterone synthesis in the prostate over a prolonged period will lead to a decreased incidence of prostate cancer. Both clinical trials offer the possibility of demonstrating that a hormonal intervention can decrease an individual's risk of developing breast or prostate cancer. They also have the potential of providing critical information about cancer risk, etiology, screening, and genetics, as well as quantifying the risks and benefits of specific preventive interventions.

5-Alpha-reductase inhibition and prostate cancer prevention.

Studies of prostate biology support the concept that dihydrotestosterone is the principal androgen responsible for normal and hyperplastic growth of the prostate gland. Cancer is a process of malignant transformation evolving over time, involving cellular growth and division. Therefore, an altered endocrine state, such as suppression of dihydrotestosterone activity, may have an impact on prostate cells inhibiting carcinogenic transformation. In vitro and in vivo preclinical observations support this hypothesis. A placebo-controlled randomized trial using finasteride, an inhibitor of the enzyme that converts testosterone to dihydrotestosterone, is planned. The endpoint of this trial will be reduction of prostate cancer incidence.

Overview of U.S. National Cancer Institute (USNCI) chemoprevention research.

The National Cancer Institute's (NCI) chemoprevention plan employs a strategy of basic and epidemiologic studies, followed by a structured preclinical process to bring chemopreventive agents into clinical testing. The field of chemoprevention is progressing rapidly and has reached the point where a coordinated international approach for large-scale trials would be useful. At present, NCI is sponsoring nine large trials (over $1 million per year per trial); in addition, nine agents are in phase I or II clinical testing. A number of these agents should be ready soon for phase III testing. Resources required for large-scale trials compel greater attention to efficient trial design, concept development and review, priority setting, management, budgeting, and collaboration.

Potential role of tamoxifen in prevention of breast cancer.

Despite advances in early detection and treatment of breast cancer, primary prevention has not been well explored, especially for women at increased risk of disease due to reproductive factors and family history. There are, however, suggestions that primary prevention of breast cancer may be a realistic objective. Randomized clinical trials of adjuvant therapy for early-stage breast cancer have demonstrated a 35% decrease in contralateral breast cancers among women receiving tamoxifen compared with controls, suggesting a potential role for tamoxifen in chemoprevention of breast cancer in women at increased risk of the disease. Adjuvant therapy studies also demonstrate that tamoxifen is well tolerated by most patients and suggest additional health benefits from alterations in plasma lipid levels and stabilization of bone mineral loss in women receiving tamoxifen. Aspects of tamoxifen pharmacology, laboratory research, and clinical experience which support its investigation as a chemopreventive agent for breast cancer are summarized, and potential toxic effects are discussed.

Early detection and control of cancer in clinical practice.

As part of the Community Cancer Care Evaluation, a random-sample survey of practicing physicians in 12 geographic areas was conducted in 1985 to provide information about physician practice patterns with reference to cancer detection, control, and treatment. All respondents were asked whether they routinely performed comprehensive physical examinations, breast palpations, mammography, rectal examinations, chest roentgenography, and stool guaiac examinations on normal healthy patients older than 50 years. Responses were examined in terms of American Cancer Society and National Cancer Institute (Bethesda, Md) recommendations. Conformity with recommendations was dependent on the geographic area, the specific procedure, and the specialty of the physician. Across all procedures, frequency of performance varied with years since graduation from medical school, with more recent graduates more likely to conform to recommended standards.

Cancer control research for community programs: the National Cancer Institute initiative.

Recognizing the need to integrate community populations into cancer control research and building on the demonstrated success of community oncologists to participate in treatment clinical trials, the Division of Cancer Prevention and Control, NCI, expanded the focus of the Community Clinical Oncology Program in 1987 to foster the development and implementation of cancer control research through the existing clinical trials network. NCI-funded cooperative groups, cancer centers, and a state health department provide research opportunities in screening and early detection, chemoprevention, smoking cessation, and continuing care. Feasibility protocols, pilot studies, and randomized clinical trials are in progress. This effort links community oncologists and other health care professionals to research in cancer control; provides access to large populations for preventive oncology studies; and establishes an effector arm for transferring current knowledge into community practices. The CCOP program is a model for maximizing available resources for future cancer control research and public health measures.

Results of a national survey of characteristics of hospital tumor conferences.

A descriptive survey of hospital tumor conferences, which are also referred to as tumor boards, was conducted by the National Cancer Institute in collaboration with the American College of Surgeons and Roswell Park Memorial Institute. The survey was done to assess the involvement of the tumor conference in the care of the patient with cancer and to lay the groundwork for additional studies of the conference. The data from the descriptive survey are based on questionnaires sent to 1,700 hospitals in the United States. The questionnaires requested information about frequency, attendance, composition, role of the chairman, agenda and other variables that relate to the format and purpose of the conference. From the results, we conclude that tumor conferences are an accepted and established institution for the multidisciplinary care of patients with cancer. They are a major source of consultation and education for physicians and for other professionals involved in oncology. Tumor conferences are conducted in a wide spectrum of hospitals and related institutions that vary in size and function.

Therapy: state-of-the-art assessment of quality. The National Cancer Institute perspective.

The National Cancer Institute (NCI) has a broad spectrum of responsibilities that range from support of basic laboratory research to the clinical testing of new therapeutics and, finally, the dissemination of results of this research to the practicing physician and the public. The reduction of cancer mortality is largely dependent on the responsibility for widespread application of state-of-the-art cancer treatments. A major cancer control focus of the NCI over the last decade has been the development and implementation of programs designed to improve awareness, access and application of state-of-the-art cancer treatment. In addition to the computerized Physician Data Query system, three targeted programs, the Cooperative Group Outreach Program (CGOP), the Community Hospital Oncology Program (CHOP), and the Community Clinical Oncology Program (CCOP) have all been aimed at establishing mechanisms to facilitate the transfer of new patient care technology; and, thereby, provide the highest quality cancer treatment in the community setting. An evaluation was conducted to determine if patterns and outcomes of cancer care management changed over time, and whether this could be related to the presence of CGOP, CHOP, and CCOP. Measurement of required program implementation was relatively straightforward. However, measurement of resultant changes in "quality of care" and the factors that influence physician performance are complex and controversial. Critical elements in the treatment of breast, colon, rectum, and small cell lung cancer were used as tracers to measure changes in the patterns of care in communities where programs were implemented. Results from this study highlight issues in state-of-the-art assessment of quality, such as the difficulty in defining quality cancer care, relationships between process and outcome indicators, and the problems of documentation and missing data. Assurance of quality cancer care requires the interaction of health care professionals with knowledge of the most up-to-date cancer research results working in a health care delivery system that encourages and rewards application of these results.