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夺去麦凯恩生命的脑癌为何如此难以医治?今后情况会如何?

Sy Mukherjee 2018年09月06日

2018年约有2.4万美国人被诊断出患有此类癌症,其中仅有三分之一左右能活过5年。

大家可能已经听说了,此前一直和恶性脑癌作斗争的参议员约翰·麦凯恩于8月25日去世,享年81岁。麦凯恩曾参加总统选举,是美国政坛传奇人物。

对于这位来自亚利桑那州的共和党人,外界高度赞誉并全面回忆了他的政治生涯和他对公众的贡献。毫无疑问,这样的举动会越来越多。但密切关注夺去麦凯恩生命的潜伏杀手同样重要——那是一种恶性脑癌,叫做多形性胶质母细胞瘤。

就统计数据而言,被诊断出胶质母细胞瘤无异于宣判死刑。脑癌和神经系统癌症通常都是致命疾病。实际上,据美国国家癌症研究所介绍,2018年约有2.4万美国人被诊断出患有此类癌症,其中仅有三分之一左右能活过5年。

美国癌症学会指出,具体来说,胶质母细胞瘤占所有脑癌和神经系统癌症的16%,有关此类病例的数字更是触目惊心: 20-44岁之间的患者(这样的病例较为罕见),其5年存活率为19%;在45-54岁的患者中,该数字下降到了8%;对于55-64岁的较高龄患者,5年存活率仅有5%,可谓机会渺茫。公开病情时麦凯恩已经80岁了(前副总统乔·拜登的儿子博·拜登同样死于该疾病,去世时年仅46岁)。

这种病为什么会这么可怕?这在很大程度上和此类肿瘤的恶性程度有关,另外还因为手术、化疗和放疗等有副作用的治疗手段存在局限性。

对此,医生、佛罗里达大学神经外科学教授杜恩·米切尔博士上周一在新闻网站The Conversation上表示:

“胶质母细胞瘤的一个额外特点是其侵略性。它的肿瘤细胞其实会慢慢脱离主要肿块,将自己深深地嵌入正常大脑中,而且经常隐藏在血脑屏障后面,这是人体的一种保护性屏障。” 米切尔写道:“这种侵略性意味着虽然神经外科手术往往可以去除胶质母细胞瘤的核心肿块,但它像手指一样的侵略性突起物会伸展到大脑的其他区域。这些游离状的癌细胞小块无法通过手术有效移除。”

因此,治疗其他类型癌症的常规方法对付不了这样聪明又恶毒的对手。同时,鉴于大脑的复杂结构及其在方方面面的关键作用,我们还看不到在很多癌症中对付胶质母细胞瘤所取得的那些进展,比如用免疫疗法或基因技术来治疗皮肤癌、肺癌和血癌。

不过,近几年科学家做出了一些(非常、非常初步)的乐观判断。美国神经外科医生协会指出,试验性胶质母细胞瘤测试正在对“基因疗法、高精度放疗、免疫疗法以及和疫苗联合进行的化疗”进行检验。但该协会也冷静地指出,这些处于早期阶段的技术平均只能将患者寿命延长三个月。(财富中文网)

译者:Charlie

审校:夏林

 

As you’ve likely heard, Sen. John McCain, former presidential candidate and a larger-than-life figure in American politics, passed away Saturday at age 81 following a battle with an aggressive form of brain cancer.

There have been plenty of tributes to and reflections on the Arizona Republican’s political career and record of public service. Those will, no doubt, continue to proliferate. But it’s also important to home in on the insidious disease that claimed McCain’s life—an aggressive form of brain cancer called glioblastoma multiforme (GBM, or just glioblastoma, for short).

A glioblastoma diagnosis, statistically speaking, amounts to a death sentence. Brain and nervous system cancers in general are deadly. In fact, just about one in three of the approximately 24,000 Americans diagnosed with such cancers in 2018 are likely to still be alive five years later, according to the National Cancer Institute (NCI).

Glioblastoma specifically makes up 16% of all brain and nervous system cancers—and the numbers are even more dire in these cases, says the American Cancer Society. If the disease manifests between the ages of 20 and 44 (a relatively rare occurrence), there’s a 19% chance of survival five years after diagnosis; among those 45 to 54, that drops to 8%; and for older Americans aged 55 to 64, the five-year relative survival rate is a dismal 5%. McCain was in his 80s when his diagnosis was publicly revealed. (Beau Biden, son of former Vice President Joe Biden, also died of the disease, but at the age of 46.)

Just why is the prognosis so dire? A lot of it has to do with just how aggressive this specific kind of tumor is, and the limitation of buzzsaw approaches such as surgery, chemotherapy, and radiation.

Dr. Duane Mitchell, a physician and professor of neurosurgery at the University of Florida, had this to say in The Conversation on Monday:

“An additional characteristic of GBM is the invasive nature of the disease. GBM tumor cells essentially crawl away from the main tumor mass and embed themselves deep within the normal brain, often hidden behind a protective barrier known at the blood-brain barrier,” Mitchell writes. “This invasive feature means that while neurosurgeons can often remove the main central tumor mass of a GBM, the invasive finger-like projections protrude into other areas of the brain. The distant islands of tumor cells that have migrated away cannot be effectively removed by surgery.”

Thus, the normal courses of treatment for other kinds of cancers may not prove effective against such a clever and malevolent foe. At the same time, the complexities of the brain’s structure—and its critical role in, well, everything—have made it so that we have yet to see the same kind of progress against glioblastoma that we have in so many cancer, such as immunotherapies and gene-based treatments for skin, lung, and blood cancers.

But scientists have sounded some (very, very early) notes of optimism in recent years. “[G]ene therapy, highly focused radiation therapy, immunotherapy, and chemotherapies utilized in conjunction with vaccines” are being tested in experimental glioblastoma trials, the American Association of Neurological Surgeons notes—while adding the sobering note that these early-stage technologies have only boosted patients’ survival rates by a median of three months.

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