The molecular approach to cancer has identified specific abnormalities that contribute to malignant pathogenesis in an aetiological manner and define individuals who are at higher risk for specific malignancies. Studies of cancer distribution in families suggest that 15-20% of all malignancies may have a significant germ line hereditable mutation that directly or indirectly contributes to tumour development. Additionally, the identification of many genetically-determined polymorphisms that regulate carcinogen metabolism indicate that their assessment may contribute to selecting individuals for preventive surveillance or intervention as well. Locating individuals in the population who have moderate to high risk germ line mutations in critical oncogenic regulatory genes and assessing a panel of polymorphisms that underlie a significant attributable risk for cancer development may allow the recruitment of individuals at high risk for a particular malignancy and, therefore, represent good candidates for either directed organ surveillance and/or chemoprevention trials.

If one were to wait for the perfect set of experimental results before launching a multi-agent chemoprevention or large risk reduction study, the trial would never be launched. On the other hand, non-scientific considerations have led to the premature launching of at least three prominent studies (CARET, Carotene and Retinol Efficacy Trial; ATBC, Apha Tocopherol Beta Carotene; PCPT, Prostate Cancer Prevention Trial) and the much delayed start-up of another, BCPT, the Breast Cancer Prevention Trial. Strong epidemiologic data by itself should not be adequate to justify starting a large trial; experimental and/or clinical data should be developed. On the other hand fear of secondary adverse events that are of low incidence should not be enough to delay a trial if the overall health benefit could be high. The development of multiagent chemoprevention trials requires that each agent is active and additively or synergistically so in combination in preclinical models. Additionally, side effects of each agent should be non-overlapping and low to non-existent, preferably a feature determined in formal phase IIa and IIb trials. These principles will be discussed in the context of prior (CARET, ATBC) and ongoing (EUROSCAN, acetylcysteine/retinol), as well as proposed future trials (difluromethyl/sulindac).

We review the current status of prevention trials in the management of cervical intraepithelial neoplasia (CIN) and cervical cancer. Two large, randomized controlled trials have shown that folic acid is inactive in reversing low to moderate grade CIN. A large randomized trial of locally applied beta-trans retinoic acid showed that the agent was effective in reversing moderate but not severe CIN. Results from a pilot trial involving 30 patients with CIN I (mild dysplasia) and CIN II (moderate dysplasia) indicate that beta-carotene can suppress CIN; a large ongoing randomized trial will answer the question more definitively.

We studied the effects of retinoids on the in vitro survival of melanoma colony-forming cells in biopsies obtained from ten patients with metastatic melanoma. The results indicate that specific retinoids reduce the ability of fresh human melanoma cells to form colonies in soft agar. The retinoids studied had differential effects on the survival of clonogenic melanoma cells, and these effects vary from patient to patient. The data provide support for the clinical trial of selected retinoids in micrometastatic and advanced melanoma.

Target populations for chemoprevention trials should include those at higher than average risk for the development of prostate cancer as defined by explicit epidemiologic and genetic criteria. Such populations include a "primary prevention" group without histologic or clinical evidence of cancer, and several clinical models of "secondary prevention," including those with clinically evident disease prior to definitive therapy and those at high risk of recurrence after therapy based on histological or biochemical status. Each risk group and clinical model has potential advantages and disadvantages, and the mechanisms that underlie disease development and progression in each group may be unique. These observations give rise to many potential clinical trials of specific agents. These trials should also include collection of data on potentially confounding influences on disease development and progression.

The risk of prostate cancer diagnosis among African Americans is 66% greater than among European American men. For African Americans with a family history of hereditary prostate cancer the increased risk of diagnosis is even greater. Thus, this population should be a prime target for chemoprevention strategies. In addition to the higher incidence of prostate cancer among African Americans compared with other populations, the mortality of prostate cancer among this high-risk population is significantly greater than 100% compared with other populations, thus further demonstrating the need for chemoprevention in this target population. Autopsy studies and clinical findings support the argument that prostate cancer exhibits more aggressive biological behavior and perhaps more rapid growth among African Americans compared with European Americans. It is hypothesized that genetic and epigenetic factors may be responsible for a more rapid growth rate among African Americans compared with other populations. Accumulating evidence indicates that a diet high in fat content is closely associated with prostate cancer progression. Investigators have reported that fat intake and percentage of energy from fat were highest in African Americans, followed by European Americans, Japanese Americans, and Chinese Americans. In conclusion, African Americans are an important target population to include in chemoprevention trials that include dietary factors as preventive agents.