ALK inhibitors are promising for treating ALK rearrangement non-small-cell lung cancer (NSCLC), but secondary mutations of ALK can sometimes inhibit their effectiveness. A 54-year-old woman with lung adenocarcinoma harboring ALK rearrangement previously treated with first-line alectinib and second-line cisplatin/pemetrexed showed poor performance status (PS) with rapid progression. She was treated with ceritinib as salvage treatment, upon which tumor shrinkage was demonstrated on CT and her PS gradually improved. The best supportive care is recommended for patients with advanced NSCLC with poor PS due to lower treatment efficacy and more toxicities than those with good PS. In this case, rapid progression led to a poor PS; however, ceritinib achieved a breakthrough in this case. The optimal treatment sequence and key drugs in ALK-positive NSCLC remain controversial.