Background: EGFR TKIs have shown first-line efficacy in EGFRm+ NSCLC but acquired resistance is inevitable; with afatinib, this is predominantly through the emergence of T790M. Therefore, a key consideration when assessing therapeutic choices is the availability of subsequent treatment options. The GioTag study (NCT03370770) is the first to assess outcomes of real-world patients (Pts) who received first-line afatinib followed by osimertinib; for pts with EGFRm+ NSCLC and acquired T790M this sequence resulted in a median time on treatment (ToT) of 27.6 months, which did not include chemotherapy. We present subgroup analyses of pts from the GioTag study who are under-represented in randomized controlled trials (RCTs) and assess the impact of afatinib treatment on ECOG PS. Methods: The GioTag study is an observational, multicenter study. Data were collected retrospectively (Dec 2017–May 2018). Pts had EGFRm+ (Del19/L858R) advanced NSCLC and acquired T790M after first-line afatinib. Pts completed afatinib and started osimertinib treatment ≥10 months before data entry to avoid early censoring and ensure mature data collection. Patient subgroups were defined based on baseline characteristics (eg, ECOG PS, age, ethnicity). The primary outcome was ToT from afatinib initiation to osimertinib discontinuation. Results: A total of 204 pts were included in the GioTag study: 15.2% had ECOG PS ≥2; 7.4% were aged ≥75 years; 8.8% were African-American. Pts generally considered to have a poor prognosis derived clinical benefit from the afatinib–osimertinib sequence: median ToT for pts with ECOG PS ≥2 (n=31) was 22.2 months (90%CI 16.0–27.0; vs pts with ECOG PS 0/1 [n=153; 31.3 months; 27.6–44.5] P<.001); and for pts aged ≥75 years (n=15), ToT was 19.9 months (9.7–not evaluable [NE]; vs pts aged <75 years [n=189; 28.1 months; 26.6–31.3] P=.382). In African-American pts, median ToT was 27.6 months (90%CI 24.7–NE). Of 180 pts with available data, 75.0% had no change or an improvement in ECOG PS from the start of afatinib to the start of osimertinib treatment; 24.4% of pts had a deterioration in ECOG PS by 1 step and 0.6% of pts had a deterioration by 2 steps. Conclusions: First-line afatinib followed by osimertinib is a feasible therapeutic strategy in pts with EGFRm+ NSCLC and acquired T790M, including those who are often under-represented in RCTs. Clinical benefit (measured by ToT) was seen among pts with poor prognosis (ECOG PS ≥2), pts aged ≥75 years, and African-American pts.