T790M may not be the only mechanism to impart EGFR TKI resistance. In addition, it is also a prognosticates long survival therefore, the patient could undergo significantly more additional chemos to make any survival benefit almost impossible to show ethically.
Afatinib had disappointing results in one of its phase III studies (although I don't recall any results presented for a confirmed T790M subgroup - I believe results based on the EGFR mutation analysis are still pending), but I'm not aware of any other failures in T790M patients - at least for agents that have shown preclinical activity against this target.
Nonetheless, if it turns out that drugs like afatinib and PF-804 lack efficacy in the T790M patients, then it won't bode well for '113.
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