Phase I trial of the MEK inhibitor selumetinib in combination with thoracic radiotherapy in non-small cell lung cancer

•Single-arm, single-centre, open-label phase I trial.•Stage III or low burden stage IV non-small cell lung cancer (NSCLC) (n = 21).•Treatment with MEK inhibitor selumetinib concomitantly with radiotherapy.•Combination feasible but outcomes poor and large incidence of pneumocystis jiroveci pneumonia. The RAS/RAF/MEK/ERK signalling pathway has a pivotal role in cancer proliferation and modulating treatment response. Selumetinib inhibits MEK and enhances effects of radiotherapy in preclinical studies. Single-arm, single-centre, open-label phase I trial. Patients with stage III NSCLC unsuitable for concurrent chemo-radiotherapy, or stage IV with dominant thoracic symptoms, were recruited to a dose-finding stage (Fibonacci 3 + 3 design; maximum number = 18) then an expanded cohort (n = 15). Oral selumetinib was administered twice daily (starting dose 50 mg) commencing 7 days prior to thoracic radiotherapy, then with radiotherapy (6–6.5 weeks; 60–66 Gy/30–33 fractions). The primary objective was to determine the recommended phase II dose (RP2D) of selumetinib in combination with thoracic radiotherapy. 21 patients were enrolled (06/2010–02/2015). Median age: 62y (range 50–73). M:F ratio 12(57%):9(43%). ECOG PS 0:1, 7(33%):14(67%). Stage III 16(76%); IV 5(24%). Median GTV 64 cm3 (range 1–224 cm3). 15 patients comprised the expanded cohort at starting dose. All 21 patients completed thoracic radiotherapy as planned and received induction chemotherapy. 13 (62%) patients received the full dose of selumetinib. In the starting cohort no enhanced radiotherapy-related toxicity was seen. Two patients had dose-limiting toxicity (1x grade 3 diarrhoea/fatigue and 1x pulmonary embolism). Commonest grade 3–4 adverse events: lymphopaenia (19/21 patients) and hypertension (7/21 patients). One patient developed grade 3 oesophagitis. No patients developed grade ≥3 radiation pneumonitis. Two patients were alive at the time of analysis (24 and 26 months follow-up, respectively). Main cause of first disease progression: distant metastases ± locoregional progression (12/21 [57.1%] patients). Six patients had confirmed/suspected pneumocystis jiroveci pneumonia. We report poor outcome and severe lymphopenia in most patients treated with thoracic radiotherapy and selumetinib at RP2D in combination, contributing to confirmed/clinically suspected pneumocystis jiroveci pneumonia. These results suggest that this combination should not be pursued in a phase II trial. ClinicalTrials.gov refere