This paper presents a rare case of an elderly patient treated with erlotinib for disseminated lung adenocarcinoma with poor performance status (Eastern Cooperative Oncology Group performance status [PS]3). This treatment led to a long duration of complete remission according to Response Evaluation Criteria in Solid Tumors 1.1 - almost 7 years (81 months) of progression-free survival (PFS) and overall survival (OS) of 10 years by March 2017. The treatment with erlotinib started in September 2008 and it was well tolerated with no adverse effects. Mutation analyses (real-time polymerase chain reaction method) revealed deletion of EGFR (epidermal growth factor receptor) gene and wild-type Kirsten-ras protein gene in exon 19. In May 2015, the patient relapsed with jaundice and enlarged lymph nodes of the liver hilum, with no other metastasis, PS 2. Biopsy confirmed metastasis of lung adenocarcinoma. EGFR molecular testing did not reveal T790M mutation. Treatment was continued with gemcitabine-cisplatin chemotherapy. A total of six cycles were administered with nearly complete response and Eastern Cooperative Oncology Group performance status 0. Further on, gemcitabine monotherapy has been administered with nearly complete response maintained and OS of 10 years by March 2017. This report describes an extremely rare case of a poor performance patient with advanced metastatic adenocarcinoma harboring EGFR mutation - deletion in exon 19 - who was receiving salvage erlotinib and had a complete response with 81 months of PFS followed by a relapse and subsequent chemotherapy which led to nearly complete response, with an OS of 10 years by March 2017. Such a complete response to tyrosine kinase inhibitor therapy in a poor PS patient, with long PFS and OS achieved, justifies tyrosine kinase inhibitor treatment approach in poor PS patients with EGFR-sensitizing tumors, and furthermore points to the feasibility of administering chemotherapy at the time of relapse.