在醫生探查人體內部情況的手段中，驗血的侵害性最小。但說到癌癥，血液就無法提供真正可靠的信息。雖然腫瘤細胞碎片確實會進入血液，但它們極為少見而且難以尋覓。因此到目前為止，醫生們了解癌癥狀況的最佳途徑是從人體內提取活體組織進行檢查。

不過，基因排序方面的新進展給癌癥液體活檢，也就是通過血液來追蹤癌癥帶來了更大的希望。在美國臨床腫瘤學會年會上，癌癥診斷公司Guardant Health的研究人員發布了令人鼓舞的研究成果。他們在1.5萬名病人身上試用了該公司覆蓋70種不同癌癥基因的檢測方法。這項技術從血液中提取微小的腫瘤DNA片段，然后對該片段進行排序，以識別腫瘤的突變類型。這有助于醫生判斷哪種治療方法對病患的癌癥最為有效，原因是許多抗腫瘤新藥都以癌癥普遍存在的突變過程為靶點。

這項研究發現，目前已獲準使用的治療藥物以及處于臨床試驗階段的實驗性藥物確實有可能對付逾三分之二病人的細胞突變。

這個研究團隊包括來自加利福尼亞大學圣地亞哥分校的科學家，他們還比較了血液檢測結果和驗血后六個月內的傳統取樣活體檢查結果。在接受測試的病人中，血液基因檢測能正確反映98%的細胞突變。

上述發現是迄今為止證明此類血液檢查能用于癌癥診斷的最有力證據。這種液體活檢優于取樣活體檢查，原因就在于眾所周知的腫瘤異質性，也就是說，同一腫瘤某處的細胞和另一處的細胞可能存在差別，而取樣檢查通常只能從某一處提取細胞。同時，腫瘤還會逐漸發生變化，但受安全和經濟性因素影響，反復進行取樣檢查并不實際。相反，血液檢查有可能長期追蹤癌癥，并能更好地反映出腫瘤出現了什么樣的變化。在腫瘤對當前治療方法產生耐藥性后，血液檢查還有可能說明需要怎樣調整治療方案。

不過，就連參與此項工作的研究人員也認為，不能說液體活檢將全面取代取樣活體檢查。要診斷癌癥，活體檢查就需要識別癌癥類型并定位原發病灶。Guardant Health聯合創始人兼首席執行官海爾米?埃爾圖基則表示：“液體活檢取代的可能是取樣活體檢查之后的所有活檢程序?！?

內布拉斯加大學醫學中心內科學教授、美國臨床腫瘤學會主席朱莉?沃斯博士指出：“可以想見這樣的檢測未來可以用于跟蹤病人的情況，并在發現新突變時調整治療方案，而且不需要對原發腫瘤進行取樣檢查。此外，在癌癥發生轉移的情況下，原發腫瘤取樣檢查可能成本較高并且較為危險?！?（財富中文網）

譯者：Charlie

審校：詹妮

A blood test is one of the least invasive ways for doctors to get a peek inside the body. But when it comes to cancer, blood isn’t exactly a reliable source of information. While tumors do shed fragments into the blood, they’re rare and hard to find, so until now, the best way for doctors to learn about tumors is to physically go in and extract snippets of them with a biopsy.

But new advances in genetic sequencing is leading to more hope for a liquid biopsy for cancer, a way to track cancer through the blood. In a study presented at the annual meeting of the American Society of Clinical Oncology, researchers from Guardant report encouraging results from a study involving 15,000 patients who were tested with the company’s test that looks at 70 different tumor genes. The technology picks up tiny fragments of DNA shed by tumors into the blood, and sequences the DNA to provide a picture of which mutations are present in the tumor. That helps doctors decide which treatments are most effective against that person’s cancer, since many of the newer anti-cancer drugs specifically target certain mutant processes common in cancer.

The study found that more than two thirds of the patients did indeed have mutations that could be addressed with currently approved drug treatments, or with experimental drugs being tested in clinical trials.

What’s more, the team of researchers, which also included scientists from University of California San Diego, also compared the blood-based results with those from a physical sample of the tumor obtained from a traditional biopsy within six months of the blood test. Among these patients, there was 98% agreement over the genetic results of which mutations were present.

Those findings are the strongest yet confirming the utility of such blood-based tests for cancer. Such liquid biopsies carry an advantage over physical biopsies since tumors are notoriously heterogeneous; cells from one part of the tumor may be different from cells from another, and biopsies typically only take cells from one part. Tumors also change over time, but repeated biopsies are not practical for safety as well as economic reasons. Blood-based testing, however, could track tumors over time and provide a better picture of how the cancer is changing, and how treatments might also have to change if the tumor is becoming resistant to an existing therapy.

But even the researchers involved in the study don’t forsee liquid biopsies replacing physical biopsies completely. In order to diagnose cancer, a biopsy is needed to establish what type of cancer is present and verify its primary location. But, says Helmy Eltoukhy, co-founder and CEO of Guardant, “what liquid biopsies might replace is every biopsy after that.”

Says Dr. Julie Vose, professor of internal medicine at the Nebraska Medical Center University Hospital and president of ASCO, “We could imagine this type of assay could be used in the future to surveil patients and change their treatments when new mutations are found, without having to biopsy the original tumor, and in cases of metastatic disease where it may be more costly and dangerous to do that.”