Brief Report: Chylothorax and Chylous Ascites During RET Tyrosine Kinase Inhibitor Therapy

INTRODUCTION

Spontaneous chylous effusions are rare; however, they have been observed by independent investigators in patients treated with RET tyrosine kinase inhibitors (TKIs).

METHODS

This multicenter, retrospective study evaluated the frequency of chylous effusions in patients treated with RET TKIs. Clinicopathologic features and management of patients with chylous effusions were evaluated.

RESULTS

A pan-cancer cohort of 7517 patients treated with one or more multikinase inhibitor or selective RET TKI and a selective TKI cohort of 96 patients treated with selpercatinib or pralsetinib were analyzed. Chylous effusions were most common with selpercatinib (7%), followed by agerafenib (4%), cabozantinib (0.3%), and lenvatinib (0.02%); none were observed with pralsetinib. Overall, 12 patients had chylothorax, five had chylous ascites, and five had both. Time from TKI initiation to diagnosis ranged from 0.5 to 50 months. Median fluid triglyceride level was lower in chylothoraces than in chylous ascites (397 mg/dL [interquartile range: 304-4000] versus 3786 mg/dL [interquartile range: 842-6596], p = 0.035). Malignant cells were present in 13% (3 of 22) of effusions. Chyle leak was not identified by lymphangiography. After initial drainage, 76% of patients with chylothorax and 80% with chylous ascites required additional interventions. Selpercatinib dose reduction and discontinuation rates in those with chylous effusions were 47% and 0%, respectively. Median time from diagnosis to disease progression was not reached (95% confidence interval: 14.5-undefined); median time from diagnosis to TKI discontinuation was 11.4 months (95% confidence interval: 8.2-14.9).

CONCLUSIONS

Chylous effusions can emerge during treatment with selected RET TKIs. Recognition of this side effect is key to prevent potential misattribution of worsening effusions to progressive malignancy.

Chylothorax and chylous ascites during RET tyrosine kinase inhibitor therapy

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Background: Spontaneous, atraumatic chylous effusions are rare. Investigators have observed a higher than anticipated incidence of chylothorax and chylous ascites in patients (pts) treated with RET tyrosine kinase inhibitors (TKIs). A systematic analysis of the occurrence of chylous effusions during RET TKI therapy and management strategies was thus performed. Methods: In this multicenter, retrospective study, the frequency of biochemically confirmed chylothorax or chylous ascites in pts treated with multikinase inhibitors (MKIs) with anti-RET activity or selective RET TKIs was determined. Clinicopathologic features and management of pts with chylous effusions were assessed. Results: A pan-cancer cohort of 7517 pts treated with at least 1 of 17 MKIs and selective RET TKIs and an independent cohort of 96 pts treated with the selective RET TKIs, selpercatinib or pralsetinib, were identified. Across cohorts, chylous effusions were identified in 22 pts and were most common with selpercatinib (7%; 15/217), followed by the MKIs agerafenib (4%; 1/24), cabozantinib (0.3%; 3/918), and lenvatinib (0.3%; 3/1185). Chylous effusions were not noted in 28 pts treated with pralsetinib. The distribution of malignancies included lung adenocarcinoma (54%) medullary thyroid carcinoma (23%), renal cell carcinoma (19%), and desmoplastic small round cell tumor (4%). Of the 22 pts, 12 had chylothorax, 5 had chylous ascites, and 5 had both. The cumulative incidence of chylous effusions from TKI initiation at 12 months was 3.09%. Median fluid triglyceride level was lower in chylothorax than in chylous ascites [397 mg/dL (IQR 282-4000) vs. 3786 mg/dL (IQR 676-6596), p = 0.035]. Median pleural fluid triglyceride level was higher with selpercatinib compared to MKIs [4,000 mg/dL (IQR 356-4425) vs. 287 mg/dL (IQR 216-395); p = 0.017]. Malignant cells were identified in the effusions from 12% (2/17) and 10% (1/10) of pts with chylothoraces and chylous ascites, respectively. Median time to disease progression from radiographic index and biochemical index across the full cohort was 1.5 years (IQR: 0.6-2.4) and 1.0 year (IQR: 0.1-1.2), respectively. Anatomic chyle leak was not identified in 6 pts who underwent lymphangiography. After initial drainage, additional drainage procedures were required in all cases with chylothorax and 50% of cases with chylous ascites. Chylous effusions prompted TKI dose reduction in 47% (7/15) of pts treated with selpercatinib and 14% (1/7) treated with MKI; none discontinued TKI due to chylous effusions. Conclusions: Chylous effusions can emerge on treatment with certain MKIs or selective RET TKIs. Recognition of this potential side effect is key to prevent misattribution of worsening effusions to progressive malignancy and to motivate a better understanding of its biology and management.

Mechanisms of acquired resistance to TRK inhibitors

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Background: First-generation TRK tyrosine kinase inhibitors (TKIs) are approved in a tumor-agnostic fashion in more than 40 countries for patients with NTRK fusion-positive adult and pediatric cancers. While resistance to these agents has previously been described, the exact frequency with which major mechanisms of resistance emerges is not clearly understood. Methods: Patients with an NTRK-fusion-positive tumor who received a first-generation TRK TKI were eligible. We retrospectively identified those patients that had post-progression tumor tissue analyzed by next-generation sequencing (NGS). The pattern of serial resistance to a second-generation TKI was analyzed when available. Results: Eighteen patients were identified. The median age was 46 years (range 2-67). Nine unique fusions were detected in ten different tumor types. NTRK1, NTRK2, and NTRK3 fusions were found in eight (44%), one (6%), and nine (50%) patients, respectively. Thirteen patients (72%) were treated with larotrectinib and five patients (28%) received entrectinib. NGS (MSK-IMPACT n = 17, Foundation One n = 1) carried out on post-progression tissue revealed the following profile of acquired resistance: on-target resistance (83%, n = 15/18), off-target resistance (11%, n = 2/18), and no identifiable mechanism (6%, n = 1/18). Among patients with on-target resistance, the most common mutation involved the solvent front (87%, n = 13/15: n = 7 NTRK3 G623R, n = 4 NTRK1 G595R, n = 1 NTRK2 G639L, n = 1 NTRK3 G623E) followed by the gatekeeper region (13%, n = 2/15: n = 1 NTRK1 F589L, n = 1 NTRK3 F617I). Two patients developed off-target alterations. One acquired BRAF V600E mutation and the other MET amplification. Interestingly, solvent front mutation loss was observed in two patients who transitioned to and progressed on a second-generation TRK TKI. One patient with a baseline NTRK1 G595R mutation developed polyclonal resistance with acquisition of KRAS G12A and NTRK1 G667A alterations as well as NTRK1 G595R loss. The other patient with NTRK3 G623R developed an NTRK3 F617I gatekeeper mutation with NTRK3 G623R loss. Conclusions: In NTRK fusion-positive cancers, on-target resistance preferentially involving the solvent front is more frequent than off-target resistance to first-generation TKI therapy. Furthermore, the sequential use of second-generation therapy appears to alter the evolutionary kinetics of mutation retention and acquisition.