Inclusion criteria:

   1. Written informed consent obtained prior to any screening procedures

   2. Age greater than or equal to 18 years old

   3. Participants with biopsy-confirmed stages IB-IVA mycosis fungoides or Sézary syndrome
   (SS). Participants with SS who have bone marrow involvement are also eligible.
   Participants with transformed CTCL are eligible

   4. Participants must have been treated with an HDAC inhibitor given for the treatment of
   CTCL. Participants must have had disease progression on or following treatment with an
   HDAC inhibitor. Participants are also eligible if they had an inadequate response to
   an HDAC inhibitor defined as stable disease as the best response after at least 3
   months of therapy. Participants previously treated with an HDAC inhibitor are also
   eligible if they experienced intolerance due to adverse events.

   5. Baseline multiple-gated acquisition scan (MUGA) or echocardiogram must have
   demonstrated left ventricular ejection fraction (LVEF) ≥ the lower limit of the
   institutional normal

   6. ECOG performance status ≤ 2

Exclusion criteria:

   1. Participants with a history of visceral disease including central nervous system (CNS)
   involvement (i.e. stage IVB CTCL). Note, participants who have SS with bone marrow
   involvement are eligible

   2. Impaired cardiac function

   3. Concomitant use of drugs with a risk of causing torsades de pointes

   4. Participants who have received chemotherapy or any investigational drug or undergone
   major surgery ≤ 3 weeks prior to starting study drug or who have not recovered from
   side effects of such therapy

   5. Less than 3 months since prior electron beam therapy

   6. Women who are pregnant or breast feeding, or women of childbearing potential (WOCBP)
   not willing to use a double method of contraception during the study and 3 months
   after the end of treatment.

Other protocol-defined inclusion/exclusion criteria may apply.