c-mabやp-mabが効かなくなる前兆としての血液変化

イタリアからの報告である。c-mabやp-mabはEGFRに対するモノクロ分子標的薬であり、大腸癌では標準治療として使われるが、いずれ抵抗性となることが多い。この抵抗性は二次的なk-ras変異によるというのが、今回のnatureの論文である。

・・・・・KRAS mutant alleles were detectable in the blood of cetuximab-treated patients as early as 10 months before radiographic documentation of disease progression・・・・

血中に遊離したがん細胞のk-ras変異は、腫瘍が再燃する時期（レントゲン上）にさかのぼること１０ヶ月前でも検索可能であるとの論旨である。

次なる手が打てる時期を確保できるという主旨であるが、面白い。

Nature(2012)

Received　08 December 2011
Accepted　23 April 2012
Published online　13 June 2012

Emergence of KRAS mutations and acquired resistance to anti-EGFR therapy in colorectal cancer

• A main limitation of therapies that selectively target kinase signalling pathways is the emergence of secondary drug resistance. Cetuximab, a monoclonal antibody that binds the extracellular domain of epidermal growth factor receptor (EGFR), is effective in a subset of KRAS wild-type metastatic colorectal cancers. After an initial response, secondary resistance invariably ensues, thereby limiting the clinical benefit of this drug. The molecular bases of secondary resistance to cetuximab in colorectal cancer are poorly understood. Here we show that molecular alterations (in most instances point mutations) of KRAS are causally associated with the onset of acquired resistance to anti-EGFR treatment in colorectal cancers.
  
  
• Expression of mutant KRAS under the control of its endogenous gene promoter was sufficient to confer cetuximab resistance, but resistant cells remained sensitive to combinatorial inhibition of EGFR and mitogen-activated protein-kinase kinase (MEK). Analysis of metastases from patients who developed resistance to cetuximab or panitumumab showed the emergence of KRAS amplification in one sample and acquisition of secondary KRAS mutations in 60% (6 out of 10) of the cases.
  
  
• KRAS mutant alleles were detectable in the blood of cetuximab-treated patients as early as 10 months before radiographic documentation of disease progression. In summary, the results identify KRAS mutations as frequent drivers of acquired resistance to cetuximab in colorectal cancers, indicate that the emergence of KRAS mutant clones can be detected non-invasively months before radiographic progression and suggest early initiation of a MEK inhibitor as a rational strategy for delaying or reversing drug resistance.