24Drs好健康報:癌症預防藥物Tamoxifen無法延長性命？
好健康熱頭條 ─ Tamoxifen作為預防藥的疑問 Tamoxifen as Prevention Questioned
好健康小單字─ 雌激素(EstrOgen)
好健康熱頭條 ─ Tamoxifen作為預防藥的疑問
最新研究顯示，大多數乳癌高風險的女性在服用癌症預防藥物tamoxifen後無法延長性命。
研究人員推斷，只有非常高風險的女性服用這種預防藥物能延長平均壽命；他們計算，美國高風險的女性如果要購買tamoxifen來延長壽命，每年將會花費130萬美元的巨大費用；這種藥在加拿大賣得比較少，每年用來救命的花費估計約為美國的十分之一。
研究人員使用電腦產生的模式讓一組假定乳癌高風險婦女來預估剩餘壽命，她們不一定有服用tamoxifen來降低風險。
加州戴維斯大學的研究人員Joy Melnikow醫師向WebMD表示，這個模式顯示，tamoxifen對於死亡率的影響力比預期少，因為它無法避免大多數因雌激素引發的致死性乳癌。
Tamoxifen是一種選擇性雌激素受體調節物（SERM）藥物，功用如同抗雌激素；雌激素會促進大多數乳癌細胞生長，所以這種藥物會針對有結合雌激素的癌細胞中所含的雌激素受體作用；它廣泛作為乳癌治療物，於1998年由藥物食品管理局核准作為乳癌高風險女性降低乳癌風險的藥物。
Melnikow醫師表示，之前從未想過事實上藉由tamoxifen以及raloxifene預防的癌症都比較容易治療，而且預後較好。
【數據】
Tamoxifen被核准作為預防藥物，依據一份政府的重大研究結果顯示，相較於沒有服藥的婦女來說，高風險婦女服藥五年能降低49%的乳癌發生率；高風險的定義是依據標準化的風險評估工具GAIL模式評估，在五年內罹患乳癌風險至少有1.67%。
然而，在最新的研究中，研究人員估計這種風險程度的女性若是缺乏雌激素受體乳癌時，死亡率確實會增加一點，缺乏雌激素受體乳癌並不是由磁激素所引起的，因此用tamoxifen沒有效。
同時，服用tamoxifen與子宮癌有關，也與增加會威脅性命的嚴重血栓風險，以及白內障有關；研究人員指出，這可能會讓乳癌風險比從tamoxifen所獲得的益處還多3%。
已經做子宮切除的女性不論風險多大，這個模式都無法顯示服用tamoxifen能讓死亡率減少多少的益處，這些服用tamoxifen的女性並未有子宮癌風險增加的情形。
Melnikow醫師與同事們在美國癌症協會於9月1日出刊的癌症（Cancer）期刊中表示，女性服用tamoxifen所獲得的預期效益接近乳癌的風險閾值1.67%，這是非常少或是根本不存在的。
Melnikow醫師向WebMD表示，在五年內有乳癌風險的女性中，不到2.5%或3%女性可能沒有服用tamoxifen，尤其是如果她們沒有做子宮切除的話更不可能服用。
【Tamoxifen與Raloxifene】
國家乳癌與大腸癌輔助性治療計劃的乳癌預防研究人員D. Lawrence Wickerham醫師向WebMD表示，少有高風險的婦女服用tamoxifen來作為預防藥物。
Wickerham醫師與同事們最近發表一篇期待已久的研究，比較更年期婦女將tamoxifen與raloxifen作為乳癌預防藥物的情形，他向WebMD表示，這篇tamoxifen與raloxifen研究（STAR）顯示，兩種藥物都同樣有效，如預期地能降低約一半的乳癌，但是raloxifen的數據顯示比較安全，導致子宮癌、血栓、以及白內障的風險較低。
Raloxifen是由Eli Lilly所製造，並以Evista品牌銷售，是普遍的骨質疏鬆症處方藥，但是尚未核准為乳癌預防藥物。
【副作用較少？】
Wickerham醫師表示，他們認為raloxifene比較好，並不是因為它比較有效，而是因為副作用比較少，Raloxifen能讓預防性治療既實用又有效，但是乳癌專家William J. Gradishar醫師並不確定，他在STAR的評論中指出，這兩種藥物的副作用差異不大，而且tamoxifen似乎能比raloxifene更能預防比較非侵入性的乳癌。
Gradishar醫師指出，雖然媒體對於之前STAR試驗數據所做的報導指出，raloxifene明顯比較好，但是臨床數據以及病患所表現出的症狀顯示兩者不相上下。
【勉強服藥】
西北大學婦科教授向WebMD表示，女性與她們的主治醫師已經減少用tamoxifen來預防癌症，他並不認為一旦raloxifene被核准後大家會改用raloxifene。
他表示，我們詢問女性是否願意每天服用一種昂貴的藥物連續五年，來降低不一定會發生的癌症風險，結果少有女性願意這麼做。
他表示，大多數人可能都不願意，除非副作用較少的乳癌預防藥物變得較為普遍，或是有比較好的方式鑑定出哪些女性比較容易罹患乳癌。
如果你想要服用這些藥物，告訴醫師有關你的乳癌風險為何。
Tamoxifen as Prevention Questioned
Most women with an elevated risk for breast cancer will not live longer if they take the cancer prevention drug tamoxifen, a new study shows.
Researchers concluded only very high-risk women benefit in terms of life expectancy when they take the drug for prevention.
They calculated that women at the lower end of the high-risk scale would spend a whopping $1.3 million per year of life added if they purchased tamoxifen in the United States. In Canada, where the drug sells for much less, the cost per year of life saved was estimated to be about one-tenth that amount.
The researchers used a computer-generated model to predict life expectancies for a hypothetical group of women at high risk for breast cancer who did and did not take tamoxifen to lower their risk.
Researcher Joy Melnikow, MD, of the University of California-Davis, tells WebMD the model showed tamoxifen had less of an impact on mortality (death) than expected because it does not protect against the most deadly breast cancers -- those not fueled by estrogen.
Tamoxifen is a selective estrogen receptor modulator (SERM) drug that works as an antiestrogen. Estrogen promotes the growth of most breast cancer cells. So the drug targets estrogen receptors on the cancer cells, which blocks estrogen from them. It is widely used as a breast cancer treatment, and was approved in 1998 by the FDA to lower breast cancer risk in women at high risk.
"The fact that the cancers prevented by tamoxifen and (the SERM) raloxifene are easier to treat and have a better prognosis really hasn't been considered before," Melnikow says.
All in the Numbers
Tamoxifen was approved for prevention, based on findings from a landmark government study in which high-risk women who took the drug for five years had a 49% reduction in breast cancer incidence, compared with women who did not.
High risk was defined as having at least a 1.67% risk of developing breast cancer within five years, based on a standardized risk assessment tool known as the GAIL model.
In the latest study, however, researchers estimated that mortality rates would actually increase slightly in women with this level of risk when the impact of estrogen-receptor negative breast cancers was considered. Estrogen-receptor negative breast cancers are not fueled by estrogen and therefore not helped with tamoxifen.
Meanwhile, tamoxifen use is associated with an increased risk for uterine cancer. Tamoxifen is also associated with increased risk for serious blood clots that can be life-threatening, and for cataracts.
The researchers concluded it would take a breast cancer risk of greater than 3% to derive a potential mortality benefit from tamoxifen.
The model did show a mortality benefit for tamoxifen users at all levels of risk if the women had had hysterectomies. The increased risk of uterine cancer from using tamoxifen does not exist for these women.
"The projected benefits of tamoxifen for women at or near the threshold risk for breast cancer of 1.67% are very small or nonexistent," Melnikow and colleagues conclude in the Sept. 1 issue of the American Cancer Society journal Cancer.
Melnikow tells WebMD that women with a five-year breast cancer risk of less than 2.5% or 3% should probably not take tamoxifen, especially if they have not had hysterectomies.
Tamoxifen vs. Raloxifene
Breast cancer prevention researcher D. Lawrence Wickerham, MD, of the National Surgical Adjuvant Breast and Bowel Project (NSABP), tells WebMD that very few women at the low end of the high-risk scale are taking tamoxifen for prevention.
Wickerham and colleagues recently reported findings from a long-awaited study comparing tamoxifen to raloxifene for breast cancer prevention in postmenopausal women.
He tells WebMD that the Study of Tamoxifen and Raloxifene (STAR) showed both drugs worked equally well, reducing breast cancers to about half of what would have been expected. But raloxifene was found to have a better safety profile, with a lower risk of causing uterine cancer, blood clots, and cataracts.
Raloxifene, which is manufactured by Eli Lilly and sold under the brand name Evista, is widely prescribed for osteoporosis, but it has not yet been approved for breast cancer prevention.
Fewer Side Effects
"We viewed raloxifene as the winner, not because it was more effective, but because it was as effective as tamoxifen with fewer side effects," Wickerham says. "Raloxifene may prove to be the drug that makes prevention treatment both practical and effective."
But breast cancer specialist William J. Gradishar, MD, is not yet convinced. In an editorial evaluating the STAR results, Gradishar noted that the difference in side effects between the two drugs was slight and that tamoxifen seemed to prevent more noninvasive breast cancers than raloxifene.
"Although media coverage of the early release of data from the STAR trial suggests a clear winner in raloxifene, the data from clinical end points and patient-reported symptoms suggest a less clear conclusion," Gradishar wrote.
Reluctance to Use Drug
The Northwestern University oncology professor tells WebMD that women and their primary care physicians have been slow to embrace tamoxifen for cancer prevention. He does not see them flocking to raloxifene once it is approved for this use.
"We are asking women to take a costly drug with potential side effects every day for five years to lower their risk for a cancer than may or may not occur," he says. "Not many women have been willing to do that."
And large numbers probably won't, he says, until better breast cancer prevention drugs with fewer side effects become available or there are better ways of identifying the women who are likely to get breast cancer.
If you're considering using one of these drugs, talk to your physician about what your breast cancer risk is.
SOURCES: Melnikow, J., Cancer, Sept. 1, 2006; vol 106: online edition. Joy Meinikow, MD, MPH, Department of Family and Community Medicine, University of California-Davis, Sacramento, Calif. D. Lawrence Wickerham, MD, associate chair of the National Surgical Adjuvant Breast and Bowel Project, National Institutes of Health. William J. Gradishar, MD, Division of Hematology/Oncology, Northwestern University, Feinberg School of Medicine, Chicago.
WebMD Medical News
by Salynn Boyles
好健康小單字─ 雌激素(EstrOgen)
雌激素又稱為動情素，是一類主要的女性荷爾蒙，包括雌酮、雌二醇等，對女性第二性徵發育扮演重要角色。好的雌激素可經由製造好的膽固醇，減少壞的膽固醇使血管保持彈性；從血流中幫助回收鈣，避免骨質疏鬆；在泌尿系統中，雌激素可增進水分滯留，保持上皮的潤滑；而當壞的或化學合成的雌激素到達乳房與乳房上皮細胞之受器相連結，則會直接影響這些上皮細胞，讓這些細胞分裂更迅速，加速乳癌細胞的生成。
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