How does cancer spread through the body? - Ivan Seah Yu Jun

癌症如何在身體各處擴散？— 依凡·夏鈺君 (Ivan Seah Yu Jun)

譯者: Regina Chu 審譯者: Geoff Chen

The onset of cancer usually begins as a solitary tumor

癌症發病通常從一個在體內

in a specific area of the body.

某特定位置的單獨腫瘤開始

If the tumor is not removed,

如果沒有移除這個腫瘤

cancer has the ability to spread to nearby organs,

癌就有能力擴散到鄰近器官

as well as places far away from the origin, such as the brain.

及離原始病灶很遠的地方 例如腦部

So how does cancer move to new areas,

所以癌怎麼移動到新的地方

and why are some organs more likely to get infected than others?

又為什麼某些器官 比較容易被浸染？

The process of cancer spreading across the body is known as metastasis.

癌在體內擴散的過程稱為轉移

It begins when cancer cells from an initial tumor invade nearby normal tissue.

它始於癌細胞從最初的腫瘤 侵入鄰近的正常細胞

As the cells proliferate,

隨著細胞增殖

they spread via one of the three common routes of metastasis:

癌藉著三個常見的途徑轉移：

transcoelomic, lymphatic, or hematogenous spread.

體腔間、淋巴或血液擴散

In transcoelomic spread, malignant cells penetrate the covering surfaces

在體腔間的擴散，惡性細胞穿透

of cavities in our body.

包覆體內空腔的表層膜

These surfaces are known as peritoneum

這種表層膜稱為腹膜

and serve as walls to segment the body cavity.

像牆般分隔體內的空腔

Malignant cells in ovarian cancer, for example,

舉例來說，卵巢癌的惡性細胞

spread through peritoneum, which connects the ovary to the liver,

就透過連接卵巢及肝的腹膜擴散

resulting in metastasis on the liver surface.

導致轉移到肝表面

Next, cancerous cells invade blood vessels when they undergo hematogenous spread.

第二，血液轉移是指 癌細胞侵入血管

As there are blood vessels almost everywhere in the body,

因為全身上下幾乎都有血管

malignant cells utilize this to reach more distant parts of the body.

惡性細胞利用這種特性 觸及到身體遠端

Finally, lymphatic spread occurs when the cancer invades the lymph nodes,

最後，淋巴轉移則在 癌細胞侵入淋巴結時發生

and travels to other parts of the body via the lymphatic system.

並經由淋巴系統 轉移到身體其他部位

As this system drains many parts of the body,

因為這個系統通到許多身體部位

it also provides a large network for the cancer.

它也為癌提供很大的傳播網路

In addition, the lymphatic vessels empty into the blood circulation,

此外，淋巴液注入血液循環

allowing the malignant cells to undergo hematogenous spread.

使得惡性細胞能藉血液傳播

Once at a new site, the cells once again undergo proliferation,

一但到了新地點 惡性細胞又開始增生

and form small tumors known as micrometastases.

形成小腫瘤，這稱為微轉移

These small tumors then grow into full-fledged tumors,

然後這些小腫瘤長大成熟

and complete the metastatic process.

完成轉移過程

Different cancers have been known to have specific sites of metastasis.

目前已知不同癌症 會轉移到不同的特定地點

For example, prostate cancer commonly metastasizes to the bone,

舉例來說，攝護腺癌 通常轉移到骨頭

while colon cancer metastasizes to the liver.

而大腸癌則轉到肝臟

Various theories have been proposed to explain the migration pattern

學者提出各種理論來解釋

of malignant cells.

惡性細胞的移動模式

Of particular interest are two conflicting theories.

特別令人感興趣的 是兩種相矛盾的理論

Stephen Paget, an English surgeon,

史蒂芬·柏哲德是英國的外科大夫

came up with the seed and soil theory of metastasis.

提出「種子與土壤」的轉移理論

The seed and soil theory stated that cancer cells die easily

種子與土壤理論說癌細胞很容易

in the wrong microenvironment,

在不對的環境中死去

hence they only metastasize to a location with similar characteristics.

因此它們只能轉移到 有相似特性的地點

However, James Ewing, the first professor of pathology at Cornell University,

但是詹姆士·尤英 康乃爾大學第一位病理學教授

challenged the seed and soil theory,

卻對這個種子與土壤理論提出挑戰

and proposed that the site of metastasis was determined by the location

並提出轉移部位是由

原發腫瘤的血液及淋巴管道 通到的位置決定

of the vascular and lymphatic channels which drain the primary tumor.

Patients with primary tumors that were drained by vessels leading to the lung

病人的原發腫瘤血管如果通到肺臟

would eventually develop lung metastases.

最終就很有可能在肺發生轉移

Today, we know that both theories contain valuable truths.

今天，我們知道這兩種理論 都有很寶貴的真理

Yet the full stories of metastasis is much more complicated

但是轉移的全盤過程

遠比這兩種提出的理論更加複雜

than either of the two proposed theories.

Factors like the cancer cell's properties,

一些因子像是癌細胞的性質

and the effectiveness of the immune system in eliminating the cancer cells,

及免疫系統消滅癌細胞的有效性

also play a role in determining the success of metastasis.

都在是否能成功轉移上扮演角色

Unfortunately, many questions about metastasis remain unanswered until today.

不幸的是，很多有關轉移的問題 至今仍然無解

Understanding the exact mechanism holds an important key

瞭解其確實的機制是重要的關鍵

to finding a cure for advanced stage cancers.

以找到後期癌症的治療法

By studying both the genetic and environmental factors,

藉由研究遺傳及環境等等

which contribute to successful metastasis,

促成轉移成功的因子

we can pinpoint ways to shut down the process.

我們能找出方法斷絕轉移過程

The war against cancer is a constant struggle,

對抗癌症的戰爭是一場持久戰

and scientists are hard at work developing new methods against metastasis.

科學家很努力地 開發新方法以對抗轉移

Of recent interest is immunotherapy,

近期備受關注的是免疫療法

a modality which involves harnessing the power of the immune system

一種物理療法 控制免疫系統的能力

to destroy the migrating cells.

以摧毀惡性細胞

This can be done in different ways,

這能以不同的方法達成

such as training immune cells to recognize cancerous cells via vaccines.

譬如以疫苗訓練 免疫細胞辨認癌細胞

The growth and activity of the immune cells

免疫細胞的成長及活動

can also be stimulated by injecting man-made interleukins,

也能以注射人工介白素來刺激

chemicals which are usually secreted by the immune cells of the body.

這種化學物質通常是由 身體的免疫細胞分泌

These two treatments are only the tip of the iceberg.

這兩種療法只是冰山一角

With the collaborated research efforts of governments, companies and scientists,

在政府、公司及科學家的 通力合作研究下

perhaps the process of metastasis will be stopped for good.

或許轉移的過程能永遠斷絕