有關乳癌和HRT之關聯的疑問


  【24drs.com】根據家庭計畫和生育保健期刊的報告指出,乳癌和荷爾蒙替代療法(HRT)的關聯是根據「不可信賴的證據」,不過,這個評論已經被參與HRT研究的專家們駁斥。
  
  作者們指出,認為雌激素加黃體素這種HRT是乳癌原因的論述,主要是根據統合再分析「Women's Health Initiative」以及「Million Women Study (MWS)」這三篇研究的結果。
  
  這些研究的結果發表於2000年初,衍生出HRT之乳癌風險的警訊,導致這些製劑的使用大幅減少。
  
  南非開普敦大學醫學院流行病學訪問教授Samuel Shapiro等作者表示,不過,這些研究並未證實因果關係,他們檢視了每項研究的一系列文獻,最新的都是聚焦在MWS。
  
  作者們指出,HRT可能會或可能不會增加乳癌風險,結論認為這些研究並未建立因果關係。
  
  作者們指出,MWS研究估計,使用HRT的乳癌風險較大,而且更甚於統合再分析或Women's Health Initiative這兩項研究,對於管理當局和大眾的安全認知有極大的影響。他們提到,「Million Women Study」是迄今最大型之HRT與乳癌的關聯研究,從其研究名稱即可知,也代表著評論的權威性。
  
  不過,單就樣本數並無法保證研究結果可信,檢視某些研究細節的效度之後,他們結論表示,MWS的證據是「不可信賴的」。Shapiro醫師等人報告指出,研究設計有缺點,也發現證據的取樣偏見和干擾,內部及外部一致性的議題與其他問題。
  
  MWS的主要研究者、英國牛津大學癌症流行病學小組Dame Valerie Beral則是駁斥這些評論,她在聲明中表示,這些不是新議題,且以前已經被推翻。
  
  她形容Shapiro醫師等人的研究,重述了許多HRT製造廠之顧問(如同這些作者)的觀點試圖駁斥有關HRT副作用的證據。
  
  作者們未提及MWS 發現HRT(特別是雌激素-黃體素複方)使用者的乳癌風險增加,現在已經有20多篇其他的研究再現,全球的整體證現已據勢不可擋。
  
  Beral醫師表示,從這些研究的結果,HRT之使用最近大幅衰減,許多國家的乳癌發生率有全國性降低。
  
  牛津大學臨床試驗服務小組共同創辦者暨共同主席Richard Peto爵士在聲明中表示,MWS提供了強力的、似是而非的因果關係,也就是說,在其他方面相似的婦女中,乳癌風險可能會增加(停藥後也可能迅速減少)。
  
  Beral醫師和Peto醫師結論表示,HRT是世界上乳癌的最重要原因之一,婦女們可藉由停藥而容易地改變風險。
  
  資料來源:http://www.24drs.com/professional/list/content.asp?x_logon=W&x_idno=6712&x_classno=0
  

Questions About Data Linking Breast Cancer and HRT

By Zosia Chustecka
Medscape Medical News

January 17, 2012 — The link between breast cancer and hormone replacement therapy (HRT) is based on "unreliable evidence," assert the authors of a paper published online January 16 in the Journal of Family Planning and Reproductive Health Care. However, this criticism has been summarily dismissed by experts involved in the HRT studies.

The authors note that the claim that HRT with estrogen plus progestogen is now an established cause of breast cancer is based principally on the findings of 3 studies — the collaborative reanalysis, the Women's Health Initiative, and the Million Women Study (MWS).

The findings from these studies, which were reported in the early 2000s, led to warnings about the risk for breast cancer from HRT, and resulted in a dramatic fall in the use of these products.

However, these studies do not prove causality, say the authors, headed by Samuel Shapiro, MB, visiting professor of epidemiology at the University of Cape Town Medical School in South Africa. They examined each of the studies in a series of articles, the latest of which focuses on the MWS.

"HRT may or may not increase the risk of breast cancer," the authors note, and conclude that these studies do not establish causality.

The MWS study estimated a larger risk for breast cancer with HRT than either the collaborative reanalysis or the Women's Health Initiative, and it had a huge impact on regulatory authorities and on the public perception of safety, the authors note. It is the largest study of HRT and breast cancer ever conducted, and its name — the Million Women Study — implies an authority beyond criticism or refutation," they add.

However, size alone dose not guarantee that the findings are reliable, they add. After examining the validity of the study in some detail, they conclude that the evidence from the MWS is "unreliable."

Dr. Shapiro and colleagues report that there were defects in the study design, and find evidence of detection bias and confounding, issues with internal and external consistency, and other problems.

However, the principal investigator of the MWS, Dame Valerie Beral, AC, DBE, FRS, MRCP, professor and head of the Cancer Epidemiology Unit at Oxford University, United Kingdom, dismissed the criticisms. "These issues are not new and have been refuted previously," she said in a statement.

She describes the paper by Dr. Shapiro and colleagues as a "restatement of views held by many consultants to HRT manufacturers (as these authors are) attempting to dispute evidence about the adverse effects of HRT."

The totality of the worldwide evidence is now overwhelming.

The authors neglect to mention that "the MWS findings of an increased risk of breast cancer in users of HRT, especially of estrogen–progestogen combinations, have now been replicated in over 20 other studies," she continued. "The totality of the worldwide evidence is now overwhelming"

"In line with the findings from these studies, the recent large decrease in HRT use has been followed in many countries by a nationwide decline in the incidence of breast cancer," Dr. Beral said.

In the related statement, Sir Richard Peto, FRS, cofounder and codirector of the Clinical Trial Service Unit, Oxford University, said that the MWS "provides strong biologically plausible evidence of causality — i.e., of an increased probability of getting breast cancer among otherwise similar women (and a rapid decrease after they stop)."

"HRT is one of the most important causes of breast cancer in the world, and women can easily change their risk by stopping," Dr. Beral and Dr. Peto conclude.

Dr. Shapiro and several coauthors report acting as consultants to manufacturers of HRT products.

J Fam Plann Reprod Health Care. Published online January 16, 2012.

    
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