ATOM: A phase II study to assess efficacy of preemptive local ablative therapy to residual oligometastases of NSCLC after EGFR TKI.

Objectives: NSCLC patients harboring EGFR mutation invariably developed resistance to EGFR TKI. We postulated that oligoresidual disease (ORD) after initial TKI might harbor resistant clones. This study aimed to test if preemptive local ablative therapy (LAT) can improve progression free survival (PFS) or not compared to historic data.

Materials And Methods: Patients indicated for EGFR TKI who possessed ORD (≤ 4 PET-avid lesions) after an initial 3-month TKI therapy were enrolled. After screening PET-CT, eligible patients with PET-avid ORDs were treated by LAT, either by stereotactic ablative radiotherapy (SABR) or surgery per clinicians' discretion. TKI was continued after LAT until it was considered ineffective. PET-CT was repeated on the 3rd and 12th month post-LAT (or at progression) apart from regular imaging. Further LAT was allowed in oligoprogressive disease. Primary endpoint was PFS rate at one-year from enrollment. Overall survival (OS), PFS and treatment safety were secondary endpoints. A post hoc comparison with screen failure cohort was performed.

Results: Eighteen patients were enrolled from 2014-17. Recruitment was stopped before the planned number (34) due to slow accrual. Two were excluded due to consent withdrawal and significant protocol violation. Median follow up was 39.1 months. Among the 16 analyzed patients, the one-year PFS rate (i.e. 15 month post TKI) was 68.8 %. Median OS was 43.3 months. All LAT were done by SABR, and none experienced ≥ grade 3 SABR related toxicities. Compared with screen failure cohort (n = 48), pre-emptive LAT effectively reduced risk of progression (HR 0.41, p = 0.0097).

Conclusion: Preemptive LAT in ORD appeared to be safe and feasible. The 1-year PFS rate was encouraging. However, potential biases and the limitations of the study should not be overlooked. Further randomized studies are warranted.