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。949Please respect copyright.ＰＥＮＡＮＡJhmEX8CdTG
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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。949Please respect copyright.ＰＥＮＡＮＡHQm7hbu4Hs
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。949Please respect copyright.ＰＥＮＡＮＡatgFlWyamT
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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。949Please respect copyright.ＰＥＮＡＮＡyWGFWDM8XL
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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。949Please respect copyright.ＰＥＮＡＮＡ2Nwsl9Z7Vo
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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。949Please respect copyright.ＰＥＮＡＮＡNGsHOcqQ6D
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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。949Please respect copyright.ＰＥＮＡＮＡQjFHurTsmi
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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)。949Please respect copyright.ＰＥＮＡＮＡoqXlOaizDb
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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。949Please respect copyright.ＰＥＮＡＮＡ1bFBdIkWzA
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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。949Please respect copyright.ＰＥＮＡＮＡ9AeoUcH64Z
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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。949Please respect copyright.ＰＥＮＡＮＡJhmhMoDfxT
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