This is a phase I/II clinical research study with BGT226, an inhibitor of phosphatidylinositol 3'-kinase (PI3K). The study consists of a Phase I dose escalation part followed by a safety expansion part and a Phase II expansion part.

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

Phase I safety expansion part will enroll advanced solid tumors. Phase II expansion part will enroll advanced breast cancer. An effort will be made to enrich the trial population with Cowden Syndrome patients with advanced solid malignancies.

Inclusion criteria:

All patients

• Histologically-confirmed, advanced solid tumors
• Progressive, recurrent unresectable disease

Phase II expansion part (advanced breast cancer)

• Confirmed positive hormone receptor (estrogen receptor and/or progesterone receptor) or positive HER-2 expression status
• Disease progression/recurrence following hormonal or anti-HER-2 treatment for advanced disease
• At least one but not more than two prior chemotherapy regimens for the unresectable tumor
• Measurable disease by MRI or CT scan

Cowden Syndrome patients with an advanced malignancy Genetic confirmation of Cowden Syndrome

• Age ≥ 18
• World Health Organization (WHO) Performance Status of ≤ 2

Exclusion criteria:

• Hematopoietic:
• No diabetes mellitus or history of gestational diabetes mellitus
• No acute or chronic renal disease
• No acute or chronic liver disease
• No acute or chronic pancreatitis
• No impaired cardiac function or clinically significant cardiac diseases such as ventricular arrhythmia, congestive heart failure, uncontrolled hypertension
• No acute myocardial infarction or unstable angina pectoris within the past 3 months
• Not pregnant or nursing and fertile patients must use barrier contraceptives

Other protocol-defined inclusion/exclusion criteria may apply.