Prolonged disease control despite ALK inhibitor discontinuation in advanced ALK-positive NSCLC

Introduction: EML4-ALK is an oncogenic driver, seen in around five per cent of advanced non-small-cell lung cancer (NSCLC) patients, which can be targeted with anaplastic lymphoma kinase tyrosine kinase inhibitors with great response rates. Disease flare refers to sudden rapid disease worsening on tyrosine kinase inhibitors (TKI) discontinuation, which is associated with shorter survival and worse outcomes. Here, we review cases previously published in the literature where patients developed disease flares, and contrast this with our patients who had prolonged survival despite TKI discontinuation. Case description: We report three different patients with advanced ALK-positive NSCLC seen at our institute, who had EML4-ALK translocation variant 1 oncogenic driver on next-generation sequencing. They received treatment with several different ALK inhibitors before opting to discontinue TKI. They were able to come off TKI safely without developing disease flare and had prolonged survival. Discussion: Shorter time to progression on TKI, presence of symptoms with disease progression or central nervous system/pleural metastasis have been previously linked with development of flare, although this was not seen in our case series. Tumour response at the time of treatment discontinuation, line of therapy, overall disease burden, fusion variant and co-alteration status can affect the prognosis of these patients after ALK TKI cessation. In particular, variant 1 and wild-type TP53 status may be a suitable patient population for dose optimisation strategies. Intermittent TKI dosing strategies may help to avoid acquiring resistance mutations and prevent long-term treatment toxicities. Conclusion: It is important for clinicians to identify patients at risk for developing disease flare on TKI discontinuation to improve outcomes. Intermittent TKI dosing strategies require further investigation.