Background: KRAS+ NSCLC remains the most common genetically defined subset of NSCLC. Despite promising pre-clinical data, MEK inhibitors have failed to provide meaningful clinical benefit both as single agents and in combination with chemotherapy in KRAS+ NSCLC patients. Pre-clinical data suggest that efficacy of MEK inhibitors in KRAS+ NSCLC differs based on specific KRAS mutations such as G12C and by status of p53 or LKB1 mutations. We conducted a phase II study to assess the efficacy of docetaxel plus trametinib in KRAS+ NSCLC patients and in specific genetic subsets. Methods:KRAS+ NSCLC patients who had progressive cancer following 1 or 2 prior regimens were eligible. Docetaxel was given at 75 mg/m2 every 3 weeks and trametinib orally at 2 mg daily. The study was 2-stage design to rule out a response rate (RR) of 17% at the 3% level with 90% power if the true rate were 37%. The study required 45 pts with a futility analysis at 30 pts; 13/45 responses would indicate a success. RR was also assessed in G12C and non-G12C cohorts and will be assessed according to presence of co-mutations in p53 and LKB1. Progression free survival (PFS) and overall survival (OS) were secondary endpoints. Multivariate analysis including age, sex, number of prior treatments, prior immunotherapy (IO) and G12C status was conducted. Results: The study enrolled 54 evaluable pts (19 G12C, 9 G12D, 9 G12A); median age 65 years; female 57%; never smokers 7%; adenocarcinoma 89%; liver metastases 31%; 2 prior regimens 70%; prior IO 57%. Outcomes are summarized in Table. Median duration of therapy was 2.2 months and most common toxicities were fatigue (78%), diarrhea (68%), nausea (57%) and vomiting (28%). One patient died of treatment related respiratory failure. There was a trend for worse PFS (HR- 1.86, p = 0.06) and survival (HR- 1.80, p = 0.14) in G12C patients. Analysis of efficacy data according to co-mutations in p53 or LKB1 is ongoing. Conclusions: Docetaxel plus trametinib met the primary endpoint of the study, with a RR of 33% and median survival of 11.1 months in patients with KRAS+ NSCLC, 70% of whom had received 2 prior regimens. Although, there was no statistical difference between KRAS+ subtypes, these data suggest that outcomes may differ between G12C and non-G12C patients. Clinical trial information: NCT02642042