Inclusion Criteria:

1. Patient has a previous diagnosis of multiple myeloma.
2. Patient requires retreatment for multiple myeloma
3. Patient has measurable M component in serum or urine at study screening

Exclusion Criteria:

1. Patient who has progressed under all prior lines of anti MM therapy
2. Patient who has been treated by bortezomib before, and did not reach at least a minor response under this therapy, or progressed under it or within 60 days of last dose
3. Patient has shown intolerance to bortezomib or to dexamethasone or components of these drugs or has any contraindication to one or the other drug , following locally applicable prescribing information
4. Patient received prior treatment with DAC inhibitors including panobinostat
5. Patient has impaired cardiac function, or a prolonged QTc interval at screening ECG
6. Patient taking medications with relative risk of prolonging the QT interval or inducing Torsade de pointes
7. Female patient who is pregnant or breast feeding or with childbearing potential and not willing to use a double method of contraception up to 3 months after the end of study treatment. Male patient who is not willing to use a barrier method of contraception up to 3 months after the end of study treatment.

Other protocol-defined inclusion/exclusion criteria may apply.