This is a first-in-human, phase I/Ib clinical research study with BEZ235, an inhibitor of phosphatidylinositol 3'-kinase (PI3K). The study consists of a dose escalation part followed by a safety dose expansion part:

Dose escalation part (advanced solid tumors, including patients with breast cancer being treated with trastuzumab):

Patients receive oral BEZ235 once daily on days 1-28 of the first course. Courses will repeat every 28 days in the absence of disease progression or unacceptable toxicity.

Cohorts of at least 3 patients receive escalating doses of BEZ235, as single agent or in combination with trastuzumab, until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose expected to produce during the first course of treatment dose-limiting toxicity in 33% of patients.

Once the MTD has been defined, the safety expansion parts of the trial will be opened for enrollment.

Safety dose expansion part (advanced solid tumors, including patients with breast cancer being treated with trastuzumab):

Patients will be treated with BEZ235, as single agent or in combination with trastuzumab, given at the MTD, once daily. Treatment of patients will continue until disease progression or occurrence of unacceptable side effects.