MA18.07 Identification of Neuroendocrine Transformation in Anaplastic Lymphoma Kinase Rearranged (ALK+) Tumors After Tyrosine Kinase Inhibitors

Acquired resistance after ALK tyrosine kinase inhibitors treatment has multiple known mechanisms: new mutations or gene amplifications, bypass signaling and rarely neuroendocrine histological transformation. Here we describe results of a program utilizing routine biopsy post-progression in ALK+ patients for clinical and research purposes. Since 2014, ALK+ lung cancer patients treated at the Princess Margaret Cancer Centre have undergone routine biopsies at disease progression time points upon failure of an ALK-tyrosine kinase inhibitor (TKI) for both clinical purposes and research purposes, in particular to obtain tissue for primary derived xenograft (PDX) engraftment. All 9/9 patients consented for research sampling during clinical biopsy procedures (median 2 extra cores/passes); 2 patients were biopsied more than once; 3 PDX models from 2 patients have engrafted; 3 additional models are too early to assess engraftment. Engraftment occurred in patients with clinically aggressive tumors and poor survival outcomes. In this process, we identified 2 patients with neuroendocrine transformation post-second generation ALK TKI: (a) a 59 yo Asian female, never smoker, diagnosed six years prior with metastatic disease, heavily pretreated with crizotinib (12 months), pemetrexed (16 months), ceritinib (25 months), alectinib (6 months) and brigatinib (3 months); post-alectinib biopsy showed no transformation, while post-brigatinib liver biopsy demonstrated transformation to large cell neuroendocrine carcinoma; (b) a 75 yo Caucasian female, never smoker, diagnosed eight months prior and started on alectinib with a partial response, progressed in a single site; endobronchial biopsy demonstrated high grade neuroendocrine transformation. Both biopsies were positive for neuroendocrine markers (chromogranin and synaptophysin), TTF-1 and diffusely co-expressed ALK on immunohistochemistry. Assessment of PDX engraftment of these models is ongoing. Routine combined clinical and research biopsy of ALK+ patients at time of TKI failure helped to identify these recent cases of neuroendocrine transformation as a possible mode of resistance and provide tissue for model development. This is the first time that ALK+ transformation to large cell neuroendocrine carcinoma is reported in the literature. (PP, AFF, SNMF, LN contributed equally).