רפואה - לא מדע מדוייק: אנטי אוקסידנטים וסרטן

בעוד שמחקרים קליניים בעבר הראו כי שימוש באנטיאוקסידנטים באנשים בריאים יכול להפחית שכיחות של גידולים מסויימים, ישנם גם מחקרים חדשים יותר שלא מוצאים אפקט הגנתי. גם לגבי האפקט של הפחתת תופעות לוואי מסויימות של רדיותרפיה וכימותרפיה ע"י אנטיאוקסידנטים דווחו לאחרונה ממצאים סותרים. יותר בעייתי הוא הנושא של שימוש באנטיאוקסידנטים בזמן טיפולי כימותרפיה ורדיותרפיה. האם זה משפר את יעילות הטיפול או מזיק לטיפול? נקודה זו לגמרי לא ברורה בינתיים ונערכים עתה הרבה ניסויים קליניים בנושא. למרות שבניסויי מעבדה על תרביות תאים ובחיות מעבדה מוצאים לעיתים שאנטיאוקסידנטים מגבירים את יעילות הטיפולים, בניסויים קליניים מבוקרים בודדים שפורסמו בספרות הרפואית מוצאים בחלקם שיפור בפרוגנוזה ובחלקם הרעה בפרוגנוזה כתוצאה מנטילת אנטיאוקסידנטים. עקב הבלבול בממצאים, אונקולוגים רבים ממליצים להמנע מלקיחת אנטיאוקסידנטים במהלך טיפולי רדיותרפיה ואף כימותרפיה. ----------------------------------------------------------- Integr Cancer Ther. 2004 Dec;3(4):333-41. Dietary antioxidants AND human cancer. Borek C. Epidemiological studies show that a high intake of anti-oxidant-rich foods is inversely related to cancer risk. While animal AND cell cultures confirm the anticancer effects of antioxidants, intervention trials to determine their ability to reduce cancer risk have been inconclusive, although selenium AND vitamin E reduced the risk of some forms of cancer, including prostate AND colon cancer, AND carotenoids have been shown to help reduce breast cancer risk. Cancer treatment by radiation AND anticancer drugs reduces inherent antioxidants AND induces oxidative stress, which increases with disease progression. Vitamins E AND C have been shown to ameliorate adverse side effects associated with free radical damage to normal cells in cancer therapy, such as mucositis AND fibrosis, AND to reduce the recurrence of breast cancer. While clinical studies on the effect of anti-oxidants in modulating cancer treatment are limited in number AND size, experimental studies show that antioxidant vitamins AND some phytochemicals selectively induce apoptosis in cancer cells but not in normal cells AND prevent angiogenesis AND metastatic spread, suggesting a potential role for antioxidants as adjuvants in cancer therapy. ---------------------------------------------------------- Cochrane Database Syst Rev. 2006 Jul 19;3:CD005037. Selenium for alleviating the side effects of chemotherapy, radiotherapy AND surgery in cancer patients. • Dennert G, • Horneber M. BACKGROUND: Selenium supplements are frequently used by cancer patients. Selenium is an essential trace element AND is involved in antioxidant protection AND redox-regulation in humans. Several adverse effects of radiotherapy AND chemotherapy in cancer patients as well as cellular processes that maintain chronic lymphoedema have been linked to oxidative cell damage in the human body. Selenium has recently been investigated as a remedy against chemotherapy AND radiotherapy-associated side effects as well as its effects on lymphoedema. OBJECTIVES: This review assessed the effects of supplementary selenium on adverse effects of conventional radiotherapy, chemotherapy, OR surgery, in oncologic patients AND on quality of life OR performance status during AND after oncologic treatment. SEARCH STRATEGY: We searched the Cochrane Pain, Palliative & Supportive Care Trials Register, the Cochrane Database of Systematic Reviews (The Cochrane Library , Issue 2, 2004), Medline (1966 - Sep 2004), Embase (1980 - 2004 week 12), SIGLE (October 2004), Cancerlit (October 2004), Clinical Contents in Medicine CCMed (October 2004), the German Register of Cancer Studies (October 2004), the NCI Clinical Trials Register (October 2004), the International Standard Randomised Controlled Trial Number Register ISRCTN (October 2004) AND the Meta-Register of Controlled Trials mRCT (October 2004), reference lists AND the archive of our working group. We contacted manufacturers of selenium supplements AND investigators. SELECTION CRITERIA: Randomised-controlled trials of selenium mono-supplements in cancer patients undergoing tumour specific therapy such as chemotherapy, radiotherapy OR surgery. DATA COLLECTION AND ANALYSIS: Two review authors independently checked trials for eligibility, extracted data AND assessed trial quality. We sought additional information from investigators when required. MAIN RESULTS: Two trials have been included, a randomised controlled trial with 60 participants at the beginning of the study investigating secondary lymphoedema AND an ongoing trial with preliminary results of 63 participants investigating radiotherapy induced diarrhoea as a secondary outcome. Both trials had drawbacks with regard to study quality AND reporting.The trial on secondary lymphoedema reported a decreased number of recurrent erysipela infections in the selenium supplementation group compared to placebo. However, results must be interpreted with caution AND cannot be generalised to other populations. The ongoing trial on radiotherapy associated diarrhoea preliminarily reported a lower incidence of diarrhoea in patients receiving selenium supplementation concomitant to pelvic radiation, however, no data were presented. Publication of final results must be awaited to discuss these findings in detail.No randomised controlled trials were found studying the effect of selenium supplementation on other therapy-associated toxicities OR quality of life OR performance status in cancer patients. AUTHORS' CONCLUSIONS: There is insufficient evidence at present that selenium supplementation alleviates the side effects of tumour specific chemotherapy OR radiotherapy treatments. Or, that it improves the after effects of surgery, OR improves quality of life in cancer patients OR reduces secondary lymphoedema. To date research findings do not provide a basis for any recommendation in favour OR against selenium supplementation in cancer patients. Potential hazards of supplementing a trace mineral should be kept in mind. ------------------------------------------------------------ Int J Cancer. 2006 Nov 1;119(9):2221-4. Antioxidant vitamins supplementation AND mortality: a randomized trial in head AND neck cancer patients. Bairati I et al. There has been concern that long-term supplementation with high-dose antioxidant vitamins, especially vitamin E (alpha-tocopherol), may increase all-cause mortality. We conducted a randomized controlled trial with alpha-tocopherol (400 IU/day) AND beta-carotene (30 mg/day) supplements among 540 head AND neck cancer patients treated by radiation therapy. Supplementation with beta-carotene was discontinued during the trial. The supplements were given during radiation therapy AND for 3 additional years. During the follow-up (median 6.5 years), 179 deaths were recorded. All death certificates were obtained. All-cause AND cause-specific mortality rates were compared between the 2 arms of the trial by Cox regression. All-cause mortality was significantly increased in the supplement arm: hazard ratio: 1.38, 95% confidence interval 1.03-1.85. Cause-specific mortality rates tended to be higher in the supplement arm than in the placebo arm. Our results concur with previous reports to suggest that high-dose vitamin E could be harmful. ------------------------------------------------------------------- Cancer Causes Control. 2006 Nov;17(9):1193-207. Prostate cancer incidence AND intake of fruits, vegetables AND related micronutrients: the multiethnic cohort study* (United States). • Stram DO et al. OBJECTIVE: To describe the relationship between the intake of fruits, vegetables, AND related vitamins AND antioxidants, AND the risk of prostate cancer in male participants in a large multiethnic cohort study. METHODS: Food AND nutrient intakes in 1993-1996 were calculated from a detailed food frequency questionnaire (FFQ) designed to account for the food AND nutrient intake of the ethnic groups represented in the study (82,486 African-American, Japanese-American, Native-Hawaiian, Latino AND White males included here). Follow-up for incident cancers utilized local SEER registries. Vital status was ascertained using state death files. Data on PSA utilization from a later questionnaire was also examined. RESULTS: A total of 3,922 incident cancer cases were ascertained during follow-up. Modestly increased risks of prostate cancer were observed in relation to higher intakes of several food items including light green lettuce AND dark leafy green vegetables. Notably, no significant protective associations of any foods were seen, including tomato intake; AND intakes of two complex foods containing tomato sauce (pizza AND Spanish rice) were associated with modest increases in risk. PSA test use was significantly AND positively related to intake of some of these same items, implying a degree of disease detection-bias. Analysis of non-localized AND high grade disease (1,345 cases) showed no significant protective associations with overall fruits AND vegetables intake, related micronutrients, OR with intake of selected complex food items. CONCLUSIONS: We found no statistically significant evidence of a protective effect against prostate cancer of higher levels of intake of any of these foods, associated micronutrients OR supplements. A possible explanation for the positive associations with risk of several of the foods normally considered to be healthy is detection bias, since "healthy" dietary intake was related to greater use of the PSA test.

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