This evidence suggests the strong clinical relevance

This evidence suggests the strong clinical relevance of the identification of acquired resistance mechanisms for a proper therapeutic decision in patients with ALK-rearranged NSCLC. When the tissue is not available, the analysis of circulating tumor DNA (cfDNA) can be a valid alternative for the determination of activating and resistance EGFR mutations. Therefore, we evaluated acquired resistance mutations associated with ALK TKI on cfDNA after the evidence of progression in patients treated with crizotinib.
Patients and Methods
Results Patient characteristics are summarized in Table 1. The analysis of cfDNA after the evidence of PD was performed before the start of new systemic treatment in 18 patients; 17 started second-generation ALK TKI treatment (12 brigatinib, 4 ceritinib, and 1 alectinib), whereas 1 patient received chemotherapy with carboplatin-paclitaxel (Table 1). Plasma was collected before stereotactic radiotherapy in 1 patient (patient 14) who was treated with continued crizotinib therapy and before best supportive care in another one (patient 20). Secondary mutations in the ALK gene were identified in 5 patients (Table 1). Three patients (patients 6, 11, and 17) were carriers of the ALK p.L1196M, p.G1269A, and p.F1174L associated with the KRAS point 5-Iodotubercidin p.G12D; 1 patient was a carrier of the p.L1196M alone (patient 12), and another one of the double ALK mutations p.L1196M and p.G1269A (patient 2; see the last paragraph of the Results section and Figures 1-3). Seven patients presented an isolated KRAS point mutation in codon 12. Post-PD samples were collected from 3 of 5 ALK-mutated patients and all showed plasmatic decreases of ALK mutations, together with tumor regression (2 objective responses and 1 stable disease according to Response Evaluation Criteria In Solid Tumors version 1.1 criteria) evidenced on computed tomography (CT) scan after 2 months of brigatinib treatment. Post-PD samples of patients 11 and 17, presented with ALK p.G1269A and p.F1174L, associated with KRAS p.G12D mutation in PD samples, were not collected because of rapid clinical worsening due to further PD. After PD during crizotinib treatment, 7 KRAS-positive patients received brigatinib, 1 ceritinib, 1 patient was treated with carboplatin-paclitaxel, and the remaining patient received best supportive care only. In 3 KRAS-positive patients (patients 3, 7, and 8) treated with brigatinib, KRAS mutation was no longer detectable in plasma DNA alongside with tumor response. In patient 6, who developed ALK p.L1196M and KRAS p.G12D during crizotinib treatment (PD sample), both mutations disappeared during treatment with brigatinib and the patient achieved tumor response. Post-PD samples were not available in patients who did not attend the clinic because of drug toxicity (patient 4) or clinical deterioration (patients 1, 10, 11, 17, and 20). Figures 1-3 show the example of patient 2, treated with crizotinib for 13 months; at PD, CT scan revealed brain and liver metastases (Figure 1A). The patient refused liver rebiopsy and only the cfDNA analysis was performed. At the time of PD there were 2 ALK mutations (p.L1196M and p.G1269A) in plasma (Figures 2A and 3). The patient started brigatinib treatment and after 2 months was reported a partial response of all the lesions (Figure 1B). Accordingly, with clinical and radiological benefit, there was a reduction of the p.L1196M mutation and the disappearance of the p.G1269A, whereas the KRAS p.G12D was acquired in cfDNA (Figures 2B and 3). In the subsequent collection of samples the KRAS mutation disappeared and the radiological partial response was maintained (Figures 2C and 3).
Discussion We report a series of 20 ALK-positive patients in whom we evaluated the presence of ALK and KRAS mutations in plasma after PD during crizotinib treatment. To our knowledge, this is the first report to evaluate the acquired resistance to ALK-TKIs using cfDNA in a cohort of crizotinib-resistant NSCLC patients. Only 2 single cases have been recently released reporting the identification of ALK mutations in plasma: 1 NSCLC patient with p.I1171N mutation who had PD during alectinib treatment and responded to ceritinib and 1 patient who had PD during crizotinib treatment with 3 resistant mutations (L1152R, I1171T, and L1196M). Data of noninvasive blood test to assess ALK mutational status are available for patients with neuroblastomas.