年度乳房攝影時的放射線曝露會增加年輕高風險婦女的乳癌風險


  【24drs.com】December 2, 2009 (芝加哥) — 根據發表於北美放射協會第95屆科學會議暨年會的新研究,年度乳房攝影檢查時的低劑量放射線曝露,會使年輕高風險婦女發生乳癌的風險更高,特別是如果她們較年輕時就開始篩檢或者篩檢頻率較高的話。
  
  六篇研究的後設分析發現,BRCA1或BCRA2基因突變婦女、或者有乳癌家族史的婦女,20歲前曝露於乳房攝影或胸部X光的放射線時,乳癌風險是未曾曝露於放射線者的2.5倍(95%信心區間[CI]為1.9- 3.2)。
  
  荷蘭Groningen大學醫學中心的Marijke C. Jansen-van der Weide博士報告指出,此分析檢視了9,420名高風險病患,還發現5次以上的乳房攝影會增加2.5倍風險(95% CI為1.6- 3.9)。
  
  Jansen-van der Weide博士表示,整體而言,相較於未曝露放射線者,曝露於低劑量放射線會增加1.5倍的乳癌風險,但不顯著。
  
  分析對象的平均年齡為45歲,她們接受的累積放射限制量範圍為0.3 -24 mSv。
  
  她向Medscape Radiology表示,希望聽眾記住的是,年輕但高風險的婦女對於乳房攝影要小心,因為她們年輕,乳房組織較緻密,這對乳房攝影來說就是一個問題;她們應考慮其他篩檢方法。
  
  婦女一生中,一般婦女約有10%的機會發生乳癌。相較之下,BRCA1基因突變的婦女有57%的機會、BCRA2基因突變婦女有49%的機會生乳癌。Jansen-van der Weide博士表示,這些婦女必須在較年輕時開始篩檢,因為許多人在30或40歲左右發生乳癌。
  
  她建議,磁振造影(MRI)是這些婦女的替代方法之一,雖然它也有一些問題,MRI並非各地皆有,需耗較多時間,比較常出現偽陽性。因此,高風險婦女和醫師就此議題的討論相當重要,雙方要一起想出篩檢策略。
  
  她強調,對於30歲以上的高風險婦女,乳房攝影篩檢不是問題。她表示,這些高風險婦女的篩檢依舊相當重要,但是,對於較年輕的婦女,我們必須考慮其他非游離輻射技術(nonionizing techniques)。
  
  根據我們的研究結果,我們討論的是20歲以下、相當年輕的婦女,我們討論的還有放射線曝露5次以上。所以,如果婦女在25歲時開始篩檢、30歲時接受5次以上乳房攝影,她的風險將會增加。30歲之前,婦女應小心,30歲之後,或許她可以兩年進行一次乳房攝影篩檢;這是一種想法。我們此次的分析只有納入6篇研究,還需要更多前瞻性研究,以更深入瞭解。
  
  會議主持人、紐約Stony Brook州立大學的Allen G. Meek醫師斷言,年經婦女的放射線風險已經充分確認。
  
  一般的共識是,尚未發育完全的乳房對於游離輻射比較敏感,所以我確信低劑量放射線的確是一個議題。
  
  他同意,婦女應和她們的醫師討論相關利益與風險。好處是早點發現癌症;風險是可能反而誘發癌症。
  
  Meek醫師向Medscape Radiology表示,此研究將使我們對於使用MRI等非游離輻射方法更有共識。他建議,25或30歲以下婦女不應進行乳房攝影,30歲之後,則應每兩年進行一次乳房攝影,或者使用MRI進行篩檢。
  
  我們知道,BCRA基因是一個放射線修補基因,若你沒有,那麼你的放射線修補能力就降低,這會讓你對低劑量乳房攝影比較敏感。我們認為,這或許是此一研究發現的生物理論基礎。
  
  Jansen-van der Weide博士以及Meek醫師皆宣告沒有相關財務關係。
  
  北美放射協會(RSNA)第95屆科學會議暨年會:摘要RO22-04。發表於2009年11月30日。

Radiation Exposure From Annual Mammography Increases Breast Cancer Risk in Young High-Risk Women

By Fran Lowry
Medscape Medical News

December 2, 2009 (Chicago, Illinois) — The low doses of radiation associated with annual screening mammography could be placing high-risk women in even more jeopardy of developing breast cancer, particularly if they start screening at a young age or have frequent exposure, according to new research presented here at the Radiological Society of North America 95th Scientific Assembly and Annual Meeting.

A meta-analysis of 6 studies found that women with BRCA1 or BCRA2 gene mutations or a family history of breast cancer who were exposed to radiation, either from mammography or chest x-rays, before the age of 20 had a risk for breast cancer that was 2.5 times higher than their counterparts who were not exposed to radiation (95% confidence interval [CI], 1.9?- 3.2).

The analysis, which examined 9420 high-risk women, also found that 5 or more mammograms increased risk 2.5-fold (95% CI, 1.6?- 3.9), Marijke C. Jansen-van?der?Weide, PhD, from the University Medical Center Groningen in the Netherlands, reported.

Overall, exposure to low-dose radiation increased breast cancer risk by a nonsignificant 1.5 times, compared with no exposure, Dr. Jansen-van?der?Weide said.

The mean age of the women in the analysis was 45 years. The cumulative dose of radiation they received ranged from 0.3 to 24?mSv.

"The take-home message here is that high-risk women who are younger should be careful about mammography screening," she told Medscape Radiology. "Because they are young, they also have dense breasts, which poses a problem with mammography. They should explore alternative screening methods."

The average woman has a 10% chance of developing breast cancer during her lifetime. In comparison, women who are carriers of the BRCA1 gene mutation have a 57% chance, and BRCA2 carriers have a 49% chance of developing breast cancer. Screening these women must start at an early age, since many will get breast cancer in their 30s or 40s, Dr. Jansen-van?der?Weide said.

Magnetic resonance imaging (MRI) could be one alternative for these women, although it has its own problems, she suggested. "MRI is not as readily available, it takes more time, and it is associated with many more false-positives. This is why it is so important for high-risk women to discuss the issue with their doctor and, together, work out a screening strategy."

She emphasized that screening mammography is not a problem for high-risk women 30 years and older. "Screening these high-risk women is still very important, but we must think about alternative nonionizing techniques at younger ages," she said.

"From our study results, we are talking about women below the age of 20, which is very young. We are also talking about 5 or more exposures. So if a woman starts at 25 and then gets 5 or more mammograms by the time she is 30, her risk will be increased. Up to the age of 30, women should be careful. After 30, perhaps she could do mammography screening every other year; that is one idea. We only used 6 studies in our analysis and we need more prospective studies to find out more about this."

The dangers of radiation in younger women have been well recognized, affirmed Allen G. Meek, MD, from State University of Stony Brook in New York, who moderated the scientific session.

"The general consensus is that the immature breast is more susceptible to ionizing radiation, so I certainly think that low-dose radiation is an issue."

He agreed that women should consider the risks and benefits and discuss them with their doctor. "The benefit is to catch the cancer earlier; the risk is you may be inducing the cancer."

Dr. Meek told Medscape Radiology that the study will make people more conscious about using a nonionizing method such as MRI. He suggested that mammograms not be done in women younger than 25 or 30 years, and then after the age of 30, a strategy might be to do a mammogram every other year, alternating with MRI.

"We know that the BRCA gene is a radiation repair gene, and when you are missing that, you have a decreased capacity for radiation repair, which will make you more susceptible to the low dose of radiation with mammography. We think this might be the biological basis for what this study found."

Dr. Jansen-van?der?Weide and Dr. Meek have disclosed no relevant financial relationships.

Radiological Society of North America (RSNA) 95th Scientific Assembly and Annual Meeting: Abstract RO22-04. Presented November?30, 2009.

    
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