Long-term efficacy and safety of larotrectinib in a pooled analysis of patients with tropomyosin receptor kinase (TRK) fusion cancer.
Authors: Drilon Alexander E. , Hong David S. , van Tilburg Cornelis Martinus , Doz Francois , Tan Daniel S.W. , Kummar Shivaani , Lin Jessica Jiyeong , McDermott Raymond S. , Zwaan C. Michel , Norenberg Ricarda , Fellous Marc Mardoche , Brega Nicoletta , Xu Rui-hua , Laetsch Theodore Willis , Shen Lin 
Published: June 2022

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Background: Neurotrophic tyrosine receptor kinase ( NTRK) gene fusions are oncogenic drivers in multiple tumors. Larotrectinib is a highly selective, central nervous system (CNS)-active tropomyosin receptor kinase (TRK) inhibitor, approved to treat adult and pediatric patients (pts) with TRK fusion cancer. In an integrated analysis of 206 pts with non-primary CNS TRK fusion cancer, larotrectinib demonstrated an investigator-assessed objective response rate (ORR) of 75%; median progression-free survival (PFS) was 35.4 months (mo; Hong et al, ASCO 2021). We report updated efficacy and safety data based on central review assessments in an expanded dataset. Methods: Data were pooled from three clinical trials (NCT02576431, NCT02122913, and NCT02637687) of pts with non-primary CNS TRK fusion cancer treated with larotrectinib. Larotrectinib was administered until disease progression, withdrawal, or unacceptable toxicity. ORR was assessed by independent review committee (IRC) per RECIST v1.1. Data cut-off was July 20, 2021. Results: As of data cut-off, 244 of 269 larotrectinib-treated pts were evaluable for efficacy by IRC. There were 25 different tumor types. The most common were soft tissue sarcoma (STS [43%], including infantile fibrosarcoma [18%] and other STS [25%]), thyroid (11%), lung (10%), salivary gland (9%), and colorectal (7% [colon, n = 18; rectal, n = 1]). Ninety-four (35%) pts were aged < 18 years; 175 (65%) were ≥18 years. Pts had gene fusions involving NTRK1 (46%), NTRK2 (3%), or NTRK3 (51%). A total of 27%, 28%, and 45% of pts had 0, 1, and ≥2 prior lines of systemic therapy, respectively. The ORR was 69% (95% confidence interval [CI] 63–75): 64 (26%) complete response (CR), including 13 (5%) pathological CR, 104 (43%) partial response,41 (17%) stable disease, 20 (8%) progressive disease, and 15 (6%) not determined. Median time to response was 1.8 mo (range 0.9–16.2). Median duration of response (DoR) was 32.9 mo (95% CI 27.3–41.7); median follow-up was 28.3 mo. Median PFS was 29.4 mo (95% CI 19.3–34.3); median follow-up was 29.3 mo. At a median follow-up of 32.2 mo, median overall survival (OS) was not reached; the 48-mo OS rate was 64% (95% CI 55–73). Treatment duration ranged from 0.1 to 67.9 months. Treatment-related adverse events (TRAEs) were mainly Grade 1–2; 50 (20%) pts had Grade 3–4 TRAEs. Five (2%) pts discontinued treatment due to TRAEs. To exclude the possible confounding effect of ongoing enrollment on median DoR, we conducted an exploratory analysis in the subset of 164 pts who were analyzed as of July 2019. The ORR was 74% (95% CI 67–81) and median DoR was 34.5 mo (95% CI 27.6–43.3); median follow-up was 34.1 mo. Conclusions: With longer follow-up, larotrectinib continued to demonstrate rapid and durable responses, extended survival benefit, and a favorable safety profile. These results highlight the importance of testing for NTRK gene fusions in cancer pts. Clinical trial information: NCT02576431, NCT02122913, NCT02637687.