Are all ALK variants created equal? Clinicopathologic features and outcomes: a propensity-matched study.

Anaplastic lymphoma kinase (ALK) rearranged NSCLC comprises a molecularly distinct subgroup occurring in 10% cases. Various EML4-ALK and non EML4 variants are known to occur which can be detected only on NGS and show differential TKI responses. 113 ALK-IHC positive cases were subjected to a custom panel-based NGS for detection of ALK variants. Clinicopathologic features and outcomes were studied and propensity-matched analysis was done. The median age of the overall cohort was 53 years. 91 (80.5%) cases were NGS positive, the most common being EML4-ALK (90, 98.9%) cases. The most common EML4 variant was Variant 1 (40, 35%) cases, Variant 3 (28, 25%) cases, and Variant 2 (17, 15%) cases. One novel EML4-ALK variant was also encountered which was found to be intrinsically resistant to crizotinib. On pre-weight-adjusted comparison, Variant 1 group had a higher occurrence of brain and extrathoracic metastases. The median OS was 44 months for the entire cohort. 49 patients received crizotinib as first-line TKI. Among these, the median OS for Variant 2 was not reached; it was 38 months and 24 months for Variant 1 and Variant 3, respectively. The median PFS for crizotinib treated patients was 8.3 months (Variant 2: 11 months, Variant 1: 8 months, and Variant 3: 9 months). On propensity-matched analyses, there was no difference in OS and PFS between Variant 1 and Variant 3, with higher HR for Variant 3. We present a large data set evaluating clinical and outcome differences between ALK variants. The unique standpoint of this study involves the propensity-weighted model to account for differences among the groups, with no prognostic differences between Variant 1 and Variant 3, which is distinct from literature.