Inclusion criteria

1. Written informed consent obtained prior to any screening procedures
2. Age ≥ 18 years old
3. Patients with biopsy-confirmed stages IB-IVA mycosis fungoides or Sézary syndrome. Patients with SS who have bone marrow involvement are also eligible.
4. Patients must have received at least two prior treatment regimens at least one of which was a systemic therapy regimen. Systemic regimens include oral bexarotene, PUVA, photophoresis, chemotherapy such as methotrexate, and interferon. Topical steroids alone are not considered as a treatment regimen.
5. Patients must have had disease progression on or following their most recent treatment regimen or an inadequate response to their most recent treatment regimen.
6. Patients will be accrued to one of two groups: Patients previously treated with oral bexarotene and patients who have not had prior oral bexarotene treatment.

Exclusion criteria

1. Prior treatment with an HDAC inhibitor.
2. Patients with visceral disease including CNS involvement (i.e. stage IVB CTCL). Note; Patients with SS who have bone marrow involvement are eligible.
3. Impaired cardiac function
4. Concomitant use of drugs with a risk of causing torsades de pointes
5. Patients who have received chemotherapy or any investigational drug or undergone major surgery < 4 weeks prior to starting study drug or who have not recovered from side effects of such therapy
6. Less than 3 months since prior electron beam therapy
7. Female patients who are pregnant or breast feeding, or patients of reproductive potential not using an effective method of birth control, and male patients whose sexual partners are women of childbearing potential not using effective birth control Other protocol-defined inclusion/exclusion criteria may apply