科普專欄–薯不揀單 - 三十秒科學–腫瘤的周遭環境

教育的氛圍及環境對兒童發展的影響極為強大，能否為下一代提供理想的學習環境，絕對是家長們需要深思的一道問題。933Please respect copyright.ＰＥＮＡＮＡdVXHuBiC5U
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同樣道理，癌細胞的周遭環境亦為它提供了有利抵禦外來藥物侵襲的能力。933Please respect copyright.ＰＥＮＡＮＡhBGs8Wa44Y
要消滅癌細胞的話，必須了解它如何與周遭環境互動，再對其加以入手。933Please respect copyright.ＰＥＮＡＮＡOlLnPyekro
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（圖2）癌細胞的周遭環境極為複雜，事實上學界不少會以「器官」而非「細胞」來冠稱癌症，皆因它與多款周遭細胞建立了不少互利關係並寄予依賴，而非以單一個體的方式生存。933Please respect copyright.ＰＥＮＡＮＡsJTdryVoic
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基於癌細胞與周遭環境互動所涉及的範圍非常之多，本篇將只會粗略講及營養及氧氣這一範疇。933Please respect copyright.ＰＥＮＡＮＡaH8fihd93O
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（圖3）血管是運送營養及氧氣的主要途徑，基於癌細胞的血管結構並不完整及參差不齊，以及腫瘤過度生長使靠近核心部份的區域遠離血管，腫瘤的某部份區域是經常性處於低氧氣及缺乏營養的狀態。933Please respect copyright.ＰＥＮＡＮＡKtX2q5BI3w
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當然，這是實體腫癌才會遇上的情景，血癌或者浮遊在血液循環系統的癌細胞則較少會面對營養或氧氣缺乏的局面。933Please respect copyright.ＰＥＮＡＮＡMyDcga96Rs
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然而，從右圖可見，距離血管超過60μm的區域已經沒有氧氣能夠抵達，而腫瘤半徑超過100μm基本上是等閒之事，所以很多時候均會把腫瘤的環境定性為低氧狀態(Hypoxia)，或完全缺氧(Anoxia)。933Please respect copyright.ＰＥＮＡＮＡwC2RNZXqns
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外來的藥物需要經由血管輸送抵達癌細胞才能發揮功用，藥物基乎無法抵達癌細胞與血管距離較遠的區域，導致藥物沒能以有效的濃度抵達腫瘤各處。933Please respect copyright.ＰＥＮＡＮＡ6mUbWyfBu4
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而且癌細胞在缺氧缺營養的狀態下，生長速度會有所減慢，這正好避過不少針對快速生長細胞特性的化療藥物追捕。933Please respect copyright.ＰＥＮＡＮＡXdDEKWyQ4R
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除藥物外，放射性治療的放射線必需依靠氧氣作為媒體才能傳遞及散播，因此這方法沒能有效根治在低氧環境下的癌細胞區域。933Please respect copyright.ＰＥＮＡＮＡQcC23fZ1d5
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