After the First TKI Fails: Sequencing Challenges in ROS1-Positive NSCLC

When a patient with ROS1-positive advanced non–small cell lung cancer (NSCLC) progresses on a first-line tyrosine kinase inhibitor (TKI), the path forward depends on factors the original treatment decision could not fully anticipate, such as the resistance mechanism, whether central nervous system (CNS) metastases are present, and whether another targeted agent or a combination with chemotherapy offers meaningful disease control. As the field evolves, the post progression landscape is thinner than it was a year ago, and the sequencing questions are more pressing.

In a virtual Case-Based Roundtable event for oncologists in the eastern United States, Bruna Pellini, MD, chief of Thoracic Medical Oncology at Baptist Health Herbert Wertheim Cancer Institute and associate professor at Herbert Wertheim College of Medicine at Florida International University, presented a second patient case focused on disease progression and sequencing after first-line entrectinib (Rozlytrek). Pellini emphasized that the data supporting current sequencing decisions were all generated in cohorts predominantly pretreated with crizotinib (Xalkori) and that the post taletrectinib era is still a data-free zone.

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This is part 2 of a 2-part series. Read part 1.

EVENT RECAP

The second case involved a patient who had received entrectinib as first-line therapy, achieved a partial response, and then developed progressive disease at approximately 17 months, consistent with the median progression-free survival (PFS) reported from the entrectinib clinical trial data. At progression, repeat molecular profiling identified a ROS1 G2032R resistance mutation, a solvent-front substitution that is one of the most commonly acquired mechanisms of TKI resistance in this disease. The patient also developed 3 new brain metastases, and the primary tumor had increased in size, representing clear systemic and intracranial progression.

When asked which second-line option they would most likely offer this patient, 71% of participants chose taletrectinib, 21% repotrectinib (Augtyro), and 7% a clinical trial. No participant chose lorlatinib (Lorbrena). The concentration of preference around taletrectinib reflected both the emerging efficacy data in the pretreated setting and the same tolerability logic that drove frontline selection in the first case. One participant articulated the reasoning clearly: “I think even if you don’t know the resistance mutation, for a patient who progressed on entrectinib, repotrectinib or taletrectinib are both reasonable options, but I’d probably go for taletrectinib and leave lorlatinib for after that.”

Pellini reviewed the available data for each agent in the pretreated setting, but observed that none of these populations were treated with identical prior therapies. In the TRIDENT-1 expansion cohort 2 (NCT03093116), repotrectinib yielded a confirmed overall response rate (ORR) of 41% in 56 TKI-pretreated patients, the majority of whom had received prior crizotinib (82%).¹ Median PFS was 8.6 months (95% CI, 6.0-not estimable), and median overall survival (OS) was 25.1 months (95% CI, 12.8-32.1). The intracranial confirmed ORR in patients with measurable brain metastases was 38%. These numbers represented a meaningful step forward from entrectinib in the post crizotinib setting, where median PFS was approximately 4.7 months and ORR was in the 11% to 18% range, but left substantial room for improvement, particularly for patients whose disease required intracranial disease control.²

Taletrectinib in the pretreated setting was studied across both TRUST I (NCT04395677) and TRUST II (NCT04919811).³ In the pooled pretreated efficacy population of 113 patients, the confirmed ORR was 55.8% (95% CI, 46.1%-65.1%), with an intracranial confirmed ORR of 65.6% (95% CI, 46.8%-81.4%). Against a backdrop of mostly crizotinib-pretreated patients in TRUST I, the ORR was 51.5%; in TRUST II, which included a population treated more heterogenously, the ORR rose to 61.7%. The intracranial activity was where taletrectinib most clearly separated from repotrectinib: 75.0% in TRUST I and 56.3% in TRUST II compared with 38% for repotrectinib in TRIDENT-1. Pellini described the near doubling of intracranial response as the most striking difference in the pretreated comparison and noted that for a patient already presenting with new brain metastases, this distinction is especially meaningful.

For patients who had received entrectinib rather than crizotinib as their prior TKI, the TRUST II data offered a rare and relevant signal. In 10 entrectinib-pretreated patients, taletrectinib produced a confirmed ORR of 80%, including 1 complete response and 7 partial responses. Among the 4 patients with measurable brain metastases in that subset, the intracranial ORR was 50%. Pellini acknowledged these are small numbers but characterized them as a genuine signal of cross-generation activity.

The durability of second-line taletrectinib response is the remaining open question. In TRUST I, median PFS in pretreated patients was 7.6 months (95% CI, 5.5-12.0) and median OS was 25.6 months (95% CI, 19.2-31.9). In TRUST II, median PFS was 11.8 months (95% CI, 7.7-19.6) and median OS had not been reached. Pellini framed the TRUST II PFS figure as numerically better than TRUST I and better than the repotrectinib second-line data, but cautioned that the shorter median follow-up of 30.5 months in TRUST II compared with 45.2 months in TRUST I limits direct interpretation.

The G2032R resistance mutation drew particular attention because it is specifically targeted by both repotrectinib and taletrectinib. In TRIDENT-1, repotrectinib produced an ORR of 58% in patients with ROS1 G2032R mutations.¹ Taletrectinib also demonstrated activity against this mutation in the TRUST II entrectinib- pretreated cohort.³ Pellini emphasized that at progression, requesting tissue or plasma molecular profiling to identify resistance mechanisms should be standard, because the G2032R mutation and potentially other resistance alterations could influence which agent is selected or whether a clinical trial targeting specific resistance mutations is appropriate.

The discussion of what comes after second-line therapy was where the group shared the most uncertainty. One participant asked whether lorlatinib, used routinely in later-line ALK-rearranged NSCLC, has a meaningful role in ROS1. Pellini acknowledged that lorlatinib does appear in the NCCN guidelines for postprogression ROS1⁴ disease but described her own practice as cautious: “I don’t know how active it would be in the post taletrectinib era; that’s an honest answer. If I’m in this situation, I call a colleague who is heavily involved in the ROS1 trials.” The group also discussed whether adding platinum-based chemotherapy to a continued TKI backbone, analogous to strategies being explored in EGFR-mutated NSCLC, represents a reasonable off-label approach at disease progression. Pellini indicated she has done this for 3 patients treated with taletrectinib and described how one patient’s insurer subsequently refused to cover both, requiring discontinuation of chemotherapy.

The most forward-looking element of the discussion was zidesamtinib, a next-generation macrocyclic ROS1 inhibitor currently available only on trial or through expanded access at select institutions.⁵ Pellini described a patient of her own who was heavily pretreated and had exhausted all standard options and is now receiving zidesamtinib through expanded access via a referral to the trial’s principal investigator. In early data, zidesamtinib has shown response rates near 44% in heavily pretreated patients, with durable responses and coverage of the G2032R resistance mutation that crizotinib, entrectinib, and currently approved agents cannot fully address.⁶ Pellini positioned it as the drug to watch for the post taletrectinib setting, with formal approval potentially this year. 

What the discussion ultimately revealed is a sequencing landscape that begins with using the most effective and tolerable targeted agent but becomes less defined with each subsequent progression. The community oncologists in this roundtable were clear-eyed about that limitation. For a patient like the one in this case, the treatment after taletrectinib is likely a clinical trial, an off-label chemotherapy combination, or a referral to a center with access to investigational agents. The signal from emerging data, however, points toward a not-distant future in which even that gap begins to close.

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DISCLOSURES: Pellini reported employment at Miami Cancer Institute; honoraria from Foundation Medicine, Merck, AstraZeneca, Regeneron, Gilead Sciences, Lilly, Bayer, Amgen, Boehringer Ingelheim, OncoHost, Jazz Pharmaceuticals; consulting or advisory roles with AstraZeneca, Regeneron, Bristol Myers Squibb/Roche, Bayer, Gilead Sciences, Foundation Medicine, OncoHost, Catalyst Pharmaceuticals, AbbVie, Boehringer Ingelheim, BlossomHill, Caris Life Sciences, Lilly, Thermo Fisher Scientific, Pfizer, Summit Therapeutics, Johnson & Johnson/Janssen; research funding from Bristol Myers Squibb, Bristol Myers Squibb Foundation (Inst), National Cancer Institute (Inst), Moffitt Cancer Center (Inst), Merck (Inst); and travel accomodations and expenses from Bristol Myers Squibb/Roche, MSD, Gilead Sciences, Regeneron.

REFERENCES:

1. Drilon A, Camidge DR, Lin JJ, et al. Repotrectinib in ROS1 fusion-positive non-small-cell lung cancer. N Engl J Med. 2024 Jan 11;390(2):118-131. doi:10.1056/NEJMoa2302299.

2. Drilon A, Siena S, Dziadziuszko R, et al. Entrectinib in ROS1 fusion-positive non-small-cell lung cancer: integrated analysis of three phase 1-2 trials. Lancet Oncol. 2020 Feb;21(2):261-270. doi:10.1016/S1470-2045(19)30690-4.

3. Pérol M, Li W, Pennell NA, Liu G, et al. Taletrectinib in ROS1+ Non-Small Cell Lung Cancer: TRUST. J Clin Oncol. 2025 Jun;43(16):1920-1929. doi:10.1200/JCO-25-00275.

4. NCCN. Clinical Practice Guidelines in Oncology. Non-Small Cell Lung Cancer. Version 5.2026. Accessed July 7, 2026. https://www.nccn.org/professionals/physician_gls/pdf/nscl.pdf 

5. Expanded Access Program of Zidesamtinib (NVL-520) for Patients With Advanced ROS1+ NSCLC or Other ROS1+ Solid Tumors. ClinicalTrials.gov. Updated June 15, 2026. Accessed July 6, 2026. https://clinicaltrials.gov/study/NCT06797362 

6. Solomon B, Popat S, Felip E, et al. Zidesamtinib efficacy and safety in patients with advanced ROS1-positive solid tumors other than NSCLC in the ARROS-1 study. J Clin Oncol. 44, 3108-3108(2026). doi:10.1200/JCO.2026.44.16_suppl.3108