Inclusion Criteria:

- Patients with confirmed HER-2 positive, metastatic or non-operable locally advanced
breast or gastric cancer

- Metastatic breast cancer patients must have received a minimum of 1 and a maximum of
3 prior anti HER2 based regimens with documented progression on the most recent
regimen which must contain trastuzumab, ado-trastuzumab emtansine or lapatinib

- Metastatic gastric cancer patients must have received a minimum of 1 and a maximum of
2 prior anti HER2 based regimens with documented progression on the most recent
regimen which must contain trastuzumab or ado-trastuzumab emtansine

- During the dose expansion part of study, all patients must have at least one
measurable lesion as defined by RECIST criteria.

- Patients must have at least one prior trastuzumab-containing regimen

- Eastern Cooperative Oncology Group (ECOG) Performance status ≤ 2

Exclusion Criteria:

- Patients with Central Nervous System (CNS) metastasis which are: symptomatic or
require treatment for symptom control and/or growing

- Prior treatment with any anti-HER3 (Human Epidermal growth factor Receptor 3)
treatment

- Impaired cardiac function

- Prior to the first dose of study treatment, patients who have received systemic
antineoplastic therapy or any investigational therapy within 4 weeks or within 5
half- lives of the therapy prior to starting study treatment, whichever is shorter,
or for cyclical therapy, within one cycle length (e.g. 6 weeks for nitrosourea,
mitomycin-C).

- Patients who have a history of primary malignancy other than that being treated in
this study, and currently requires active clinical intervention.

- Patients who do not have an archival tumor sample (or sections of it) available or
readily obtainable.

Other protocol-defined inclusion/exclusion criteria may apply