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JAMA:大豆蛋白补充剂不降低前列腺切除术后前列腺癌复发

  1. 前列腺癌丨 前列腺切除 丨 大豆蛋白补充剂

来源:MedSci 2013-07-11 21:00

据7月10日发表在《美国医学会杂志》上的一则研究披露,在那些接受了根治性前列腺切除术的男性中,每日进食一种含有大豆蛋白分离物饮料粉补充剂达2年的人与那些只接受安慰剂的男性相比,其前列腺癌生化复发的出现并没有减少或推迟。

据7月10日发表在《美国医学会杂志》上的一则研究披露,在那些接受了根治性前列腺切除术的男性中,每日进食一种含有大豆蛋白分离物饮料粉补充剂达2年的人与那些只接受安慰剂的男性相比,其前列腺癌生化复发的出现并没有减少或推迟。(JAMA. 2013;310(2):170-178)

根据文章的背景资料:“在美国及其它西方国家,前列腺癌是最常被诊断的恶性肿瘤及第二常见的男性癌症死亡原因,但它在亚洲国家的出现频率却低得多。在观测研究中,前列腺癌风险与大豆及大豆食品的摄入呈负相关,而这也许能解释这种地理差异,因为在美国的大豆进食量低而在亚洲国家则高。”

“… 不存在大豆补充剂对这些男性具有任何的前列腺癌相关性裨益的证据。大豆含有的几种成分——其中包括大豆异黄酮——在实验室研究中具有抗癌活性。”

伊利诺伊大学芝加哥分校的Maarten C. Bosland, D.V.Sc., Ph.D.及其同事对每日进食某种基于大豆蛋白的补充剂是否能在接受了根治性前列腺切除术后有复发高风险的男性中降低其前列腺癌的复发率或延迟其复发进行了检查。这一随机试验是在1997年7月至2010年5月间在美国的7个医疗中心内开展的,其中包括了177名男性。补充剂干预是在手术后4个月内开始的并持续每日服用长达2年;在第一年中,前列腺特异性抗原(PSA)的检测间隔为每2个月,此后为每3个月检测一次。参与者被随机指派接受每日服用含有20克以大豆蛋白分离物的(n=87)饮料粉或含有酪酸钙的安慰剂(n=87)饮料粉。

该试验因为在一个按计划进行的中期分析过程中缺乏治疗效果而被提前终止;在该分析包括了81位可供评估的干预组参与者及78名安慰剂组的参与者。总体而言,有28.3%的参与者在进入该试验后2年内出现了生化性复发(定义为出现PSA浓度≥0.07 ng/mL)。在干预组参与者中有22人(27.2%)出现了得到确认的生化性复发,而服用安慰剂的参与者中有23人(29.5%)出现了复发。文章的作者写道:“在出现复发的参与者中,复发时间的中位数[中点]在干预组中(31.5周)似乎要比在安慰剂组中(44周)稍短些,但这一差异没有统计学意义。”

参与者的依从性大于90%。2组发生的不良事件之间没有差别。

研究人员写道:“本研究的结果为人们提供了又一个例子,即观察性的流行病学研究中的据称的预防性制剂和临床结果之间的关系需要通过随机性的临床试验进行确认。这些结果不仅与进食大豆与前列腺癌风险的流行病学证据不符,而且它们也与前列腺肿瘤发生的动物模型试验结果不一致——动物模型试验结果也提示了复发风险会下降。”

这些矛盾结果的一个可能的解释是,在流行病学研究及动物实验中,大豆接触通常出现在研究参与者或动物寿命中的大多数时间或全部时间中;在这类研究中没有报告指出大豆接触是在生命的较晚时期开始的。因此可以想得到,在生命早期就开始进食大豆时,大豆具有抗前列腺癌的保护作用,但这种保护作用不会出现在生命的晚期或当前列腺癌已经存在的时候。如果真是这种情况,鉴于在中年男性中未被发现的前列腺癌具有高发生率,那么在生命的较晚时期开始用大豆对前列腺癌进行防癌治疗就不太可能有效。(生物谷Bioon.com)

生物谷推荐英文摘要:

Jama      doi:Jama/ 2013;310(2):170-178

Soy Protein Supplementation Does Not Reduce Risk of Prostate Cancer Recurrence After Radical Prostatectomy

CHICAGO – Among men who had undergone radical prostatectomy, daily consumption of a beverage powder supplement containing soy protein isolate for 2 years did not reduce or delay development of biochemical recurrence of prostate cancer compared to men who received placebo, according to a study in the July 10 issue of JAMA.

“Prostate cancer is the most frequently diagnosed malignancy and the second most frequent cause of male cancer death in the United States and other Western countries but is far less frequent in Asian countries. Prostate cancer risk has been inversely associated with intake of soy and soy foods in observational studies, which may explain this geographic variation because soy consumption is low in the United States and high in Asian countries,” according to background information in the article.

“Although it has been repeatedly proposed that soy may prevent prostate cancer development, this hypothesis has not been tested in randomized studies with cancer as the end point. A substantive fraction (48 percent – 55 percent) of men diagnosed as having prostate cancer use dietary supplements including soy products, although the exact proportion is not known. However, no evidence exists that soy supplementation has any prostate cancer-related benefits for these men. Soy contains several constituents, including isoflavones, which possess anticancer activities in laboratory studies.”

 

Maarten C. Bosland, D.V.Sc., Ph.D., of the University of Illinois at Chicago, and colleagues examined whether daily consumption of a soy protein-based supplement would reduce the rate of recurrence or delayed recurrence of prostate cancer in men at high risk of recurrence after radical prostatectomy. The randomized trial was conducted from July 1997 to May 2010 at 7 U.S. centers and included 177 men. Supplement intervention was started within 4 months after surgery and continued daily for up to 2 years, with prostate-specific antigen (PSA) measurements made at 2-month intervals in the first year and every 3 months thereafter. Participants were randomized to receive a daily serving of a beverage powder containing 20 g of protein in the form of either soy protein isolate (n=87) or as placebo, calcium caseinate (n=90).

The trial was stopped early for lack of treatment effects at a planned interim analysis with 81 evaluable participants in the intervention group and 78 in the placebo group. Overall, 28.3 percent of participants developed biochemical recurrence (defined as development of a PSA level of ≥0.07 ng/mL) within 2 years of entering the trial. Twenty two (27.2 percent) of the participants in the intervention group developed confirmed biochemical recurrence, whereas 23 (29.5 percent) of the participants receiving placebo developed recurrence. “Among participants who developed recurrence, the median [midpoint] time to recurrence was somewhat shorter in the intervention group (31.5 weeks) than in the placebo group (44 weeks), but this difference was not statistically significant,” the authors write.

Adherence was greater than 90 percent. There were no differences in adverse events between the 2 groups.

“The findings of this study provide another example that associations in observational epidemiologic studies between purported preventive agents and clinical outcomes need confirmation in randomized clinical trials. Not only were these findings at variance with the epidemiologic evidence on soy consumption and prostate cancer risk, they were also not consistent with results from experiments with animal models of prostate carcinogenesis, which also suggest reduced risk,” the researchers write.

“One possible explanation for these discrepant results is that in both epidemiologic studies and animal experiments, soy exposure typically occurred for most or all of the life span of the study participants or animals; there are no reports of such studies in which soy exposure started later in life. Thus, it is conceivable that soy is protective against prostate cancer when consumption begins early in life but not later or when prostate cancer is already present. If this is the case, chemoprevention of prostate cancer with soy is unlikely to be effective if started later in life, given the high prevalence of undetected prostate cancer in middle-aged men.”

 

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