Sixteenth Aspen Cancer Conference: Mechanisms of Carcinogenesis, Cancer Prevention, and Cancer Therapy.
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During the last three decades, the scientific community has made immense progress in acquiring the knowledge needed to prevent cancer. Pioneering research helped to identify potential causes of cancer, particularly environmental factors such as diet, and provided insight regarding their mechanisms-of-action. Concurrently, promising inhibitors of cancer that appeared able to either arrest or reverse cancer development by interfering with one or more steps in the process of carcinogenesis were identified and systematically evaluated for their potential as chemopreventive agents. Numerous agents determined to be safe and effective in preclinical trials have been and continue to be tested in Phase I,II, and III clinical interventions for cancers at various sites, including breast, colon, prostate, esophagus, mouth, lung, cervix, endometrium, ovary, liver, bladder, and skin. The development of valid intermediate biomarkers that can serve as surrogate endpoints for clinical disease is urgently needed to accelerate advances in clinical trials for cancer prevention.
Preventing cancer saves the labor of mending social, economic, cultural, and emotional upheaval engendered by a diagnosis of cancer. The four position statements discussed in this article provide a wealth of perspective regarding the professional organizations' views on cancer prevention and the important roles of nurses.
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Herbal medicines are now attracting attention as potential sources of cancer preventive agents. Using inhibition of tumor necrosis factor-alpha (TNF-alpha) release assay, we studied Acer nikoense, Megusurino-ki in Japanese. Inhibitory potential was found in the leaf extract, and the main active principles were identified as geraniin and corilagin. The IC(50) values for TNF-alpha release inhibition were 43 microM for geraniin and 76 microM for corilagin, whereas that for (-)-epigallocatechin gallate (EGCG), the green tea polyphenol, as control was 26 microM. Furthermore, treatment with geraniin inhibited okadaic acid tumor promotion in a two-stage carcinogenesis experiment on mouse skin. Geraniin and corilagin are present in another well-known Japanese traditional herb, Geranium thunbergii, Genno-shoko in Japanese. Considering seasonal variations of the agents and sites of cultivation of herbs, this paper reviews the significance of geraniin as a new cancer preventive agent. In addition, based on accumulated results of green tea as a cancer preventive, we review two important results with EGCG: the synergistic effects of EGCG with sulindac or tamoxifen on cancer preventive activity in PC-9 cells, and cancer prevention of intestinal tumor development in multiple intestinal neoplasia (Min) mice by cotreatment using EGCG with sulindac. We report here new findings on additional gene expression resulting from cotreatment with EGCG and sulindac in PC-9 cells compared with gene expression by EGCG alone or sulindac alone. Overall, our results indicate that, with the continuing spread of cancer chemoprevention as a fundamental medical strategy, both clinicians and researchers should take a closer look at herbal medicine.
The Cancer Research Foundation of America has played a key role in "fueling the engine" of cancer prevention progress through a national research grant and education program. It is one of the nation's leading cancer prevention organizations, and has helped move prevention science from the fringes to the mainstream. Since its inception in 1985, it has provided more than $42.1 million in funding for cancer prevention research and education. It has supported pioneering research and translated it into practical information to educate men, women, and children about how to reduce their cancer risk. As more and more research results in practical interventions to prevent cancer, the Foundation will continue to act in an anticipatory way to help smooth the way for rapid translation of information from scientific study to consumer information through education and awareness initiatives. As we celebrate our 15th anniversary, the Cancer Research Foundation of America has recommitted itself to its role as a catalyst for change. It hopes to help the nation move toward a future in which harsh and often toxic treatment for cancer is replaced with a sane policy of cost-effective early intervention-healthy lifestyle education, detection of premalignant conditions, and therapies that spare healthy tissue. The Foundation believes there is a groundswell of support for making cancer prevention and early detection a national priority.
The retinoid skin cancer prevention (SKICAP) trials are a set of double-blind, randomized, placebo-controlled clinical trials. The SKICAP-actinic keratoses (AK) trial tests the hypothesis that daily supplementation of retinol (25,000 IU) for 5 years reduces the incidence of skin cancers in high-risk individuals, those with a history of greater than ten clinically or pathologically diagnosed AK and, at most, one prior pathologically confirmed cutaneous squamous cell carcinoma (SCC) or basal cell carcinoma (BCC). The SKICAP-SCC/BCC (S/B) trial tests the hypothesis that daily supplementation of retinol (25,000 IU) or 13-cis-retinoic acid (5 or 10 mg) for 3 years reduces skin cancer incidence in very high-risk individuals, those with a history of at least four pathologically confirmed SCCs or BCCs. Between 1984 and 1988, 2800 participants were enrolled at two clinics on the SKICAP-AK trial; and between 1985 and 1990, a total of 719 participants were enrolled at four clinics on the SKICAP-S/B trial. The initial recruitment strategy was referral by dermatologists, but low accrual necessitated the use of other strategies to achieve enrollment goals, which included involving additional clinics and using paid trial-specific advertisements in print and electronic media. Thirteen % of the SKICAP-AK participants and 36% of the SKICAP-S/B participants were enrolled through dermatologist referral, whereas paid advertisements resulted in enrollment of 87% of SKICAP-AK and 43% of SKICAP-S/B participants. A population-based skin cancer registry was used to identify and enroll the remaining 21% of the SKICAP-S/B participants.(ABSTRACT TRUNCATED AT 250 WORDS)
The above comments only partially reflect current research and interventions in cancer prevention, but they do lead to at least two simple conclusions: first, we are at an embryonic stage in the development of cancer prevention activities. Although the reasons for this are somewhat arcane and complex, it is nevertheless disappointing. Second, there is a growing commitment to and enthusiasm for prevention activity, albeit it to differing degrees and at different levels. In many centers it appears that there is interest, and while ill-defined, there is evidence for the search for structure and function. This is even being reinforced with the allocation of resources. On the other hand, several centers have already made the commitment, and seemed to have gained the respect of the scientific community both intra and extramurally in their respective orientations.
The Breast Cancer Prevention Trial (P-1: BCPT) of the National Surgical Adjuvant Breast and Bowel Project (NSABP) randomized 13,388 women, > or = 35 years of age, at increased risk for breast cancer [> or = 1.66% by Gail model criteria or with a history of lobular carcinoma in situ (LCIS)] to 5 years of tamoxifen or placebo. A 49% reduction (P < 0.00001) in invasive breast cancers occurred, 175 with placebo versus 89 with tamoxifen, mainly among estrogen receptor (ER)-positive tumors (130 with placebo vs. 41 with tamoxifen). The major toxicities of tamoxifen were endometrial cancer (15 with placebo vs. 36 with tamoxifen) and thromboembolic disease, both predominantly in women who were > or = 50 years old. Ramifications emerging from the P-1 results regarding the efficacy and toxicities of preventive tamoxifen include the following: (1) Does tamoxifen induce more virulent breast cancers? (2) Does tamoxifen induce more virulent endometrial cancers? (3) Tamoxifen is especially efficacious in reducing breast cancer risk in LCIS (18 invasive breast cancers with placebo vs. 8 with tamoxifen group) and atypical ductal hyperplasia (AH) (23 invasive breast cancers with placebo vs. 3 with tamoxifen). (4) Does tamoxifen reduce breast cancer risk in women at increased risk due to genetic mutations? (5) How can we prevent tamoxifen-resistant breast cancers? (6) What do the BCPT results tell us about who should take preventive tamoxifen? In its ongoing effort to lower the incidence of breast cancer, the NSABP is now implementing its second breast cancer prevention trial, the Study of Tamoxifen and Raloxifene (STAR), which is comparing the two agents with regard to efficacy and toxicity.
Many cancer prevention strategies are unlikely to provide equal risk reduction in all subjects, but instead are predicted to be particularly useful for specific individuals. An important research challenge is to devise methods for individualization of cancer prevention recommendations, such that particular interventions are assigned to those who will gain the most. Research in this area is at an early stage, but progress that allows rational assignment of specific prevention strategies to particular individuals who will benefit would decrease the cost, minimize the toxicity, and increase the efficacy of interventions intended to prevent cancer.
The Prostate Cancer Prevention Trial was the first clinical trial to show that a direct intervention (5 mg of finasteride daily for 7 years) could reduce a man's risk of developing prostate cancer. Initial results also suggested that men taking finasteride had an increased risk of developing what appeared to be higher-grade disease (Gleason score 7-10). The National Cancer Institute has a congressional mandate to communicate health information to the public and has established methods to reach the public directly and to reach information intermediaries in the media, professional societies, and advocacy groups. The groundbreaking yet complicated results of the Prostate Cancer Prevention Trial were widely disseminated by National Cancer Institute using the social marketing and public-relations strategies and tactics detailed here.