Background: Resistance to mTORC1 inhibition may develop through feedback loop leading to upregulation of mTORC2. XP-105, also known as BI 860585, is a potent dual mTORC1/2 inhibitor designed to overcome such resistance. This Phase 1 trial (NCT01938846) was performed to determine the MTD and activity of XP-105 alone or in combination with exemestane or paclitaxel in pts with advanced solid tumors. Methods: A 3+3 escalation design was used; Pts received XP-105 (5–300 mg/day) monotherapy or (40–220 mg/day) combined with fixed-dose exemestane 25 mg/day, or 80–160 mg/day combined with paclitaxel 60 or 80 mg/m²/week. A reduction of pAKT/total AKT ratio was used as a PD marker of target inhibition. Results: 90 pts were treated (41 with monotherapy, 25 and 24 in combination with exemestane, or paclitaxel respectively). XP-105 MTD was defined as 220 mg daily for monotherapy, and 160mg daily with exemestane 25 mg/d or paclitaxel 80 mg/m²/week. In the monotherapy arm, stable disease (SD) was reported in 8 pts (20%), with a median duration of 11 months. In the exemestane combination arm, 4 (16%) partial responses (PR) were reported. In the paclitaxel combination arm, 1 complete response (CR) and 4 PRs were reported (OR rate 21%). Disease control rate (CR/PR/SD) was 20%, 28%, and 58% in the monotherapy, XP-105/exemestane, and XP-105/paclitaxel arms, respectively. A sustained reduction in pAKT/total AKT to < 50% of baseline levels was observed with XP-105 ≥120mg daily. Overall, XP-105 was well tolerated; in the XP-105/paclitaxel combination the most frequent drug-related AEs were diarrhea and fatigue (58.3% each), hyperglycaemia (54.2%), anaemia (50%). Grade ≥3 AEs were hyperglycaemia, fatigue, diarrhea, anaemia, leukopenia. No PK interaction was observed. Conclusions: The MTD for XP-105 monotherapy and in combination with exemestane or paclitaxel was defined as 220 mg and 160mg once daily, respectively. Combination regimens showed higher activity as compared to monotherapy with durable OR in about 20% of pts. The observed safety profile of XP-105 compared favorably to those reported from other mTOR inhibitors. Clinical trial information: NCT01938846