<br>        Key Inclusion Criteria:<br><br>          -  Diagnosis of LGS carcinoma of the ovary, fallopian tube or primary peritoneum<br>             (invasive micropapillary serous carcinoma or invasive grade 1 serous carcinoma),<br>             confirmed histologically and verified by central pathology review.<br><br>          -  Recurrent or persistent measurable disease that has progressed (defined as<br>             radiological and/or clinical progression; an increase in cancer antigen [CA]-125 alone<br>             is not sufficient) on or after last therapy (i.e., chemotherapy, hormonal therapy,<br>             surgery) and is not amenable to potentially curative intent surgery, as determined by<br>             the patient's treating physician.<br><br>          -  Must have received at least 1 prior platinum-based chemotherapy regimen but have<br>             received no more than 3 lines of prior chemotherapy regimens, with no limit to the<br>             number of lines of prior hormonal therapy. Front-line therapy may include neoadjuvant<br>             and adjuvant therapy and will be counted as 1 prior systemic regimen. Biological<br>             therapy (e.g. bevacizumab) administered as a single agent is considered a prior<br>             systemic regimen and not a prior chemotherapy regimen. Maintenance therapy is not<br>             considered its own regimen but should be included with the regimen that it follows.<br><br>          -  Available archival tumor sample (excisional or core biopsy) for confirmation of LGS<br>             carcinoma diagnosis. If adequate archival tumor sample is not available, willingness<br>             to consent to tissue biopsy.<br><br>          -  Suitable for treatment with at least one of the physician's choice chemotherapy<br>             options (liposomal doxorubicin, paclitaxel or topotecan) as determined by the<br>             Investigator.<br><br>          -  Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1.<br><br>          -  Additional criteria exist.<br><br>        Key Exclusion Criteria:<br><br>          -  History or current evidence of retinal vein occlusion (RVO) or current risk factors<br>             for RVO (e.g., uncontrolled glaucoma or ocular hypertension, history of hyperviscosity<br>             or hypercoagulability syndromes).<br><br>          -  Prior therapy with a MEK or BRAF inhibitor.<br><br>          -  History of Gilbert's syndrome.<br><br>          -  Impaired cardiovascular function or clinically significant cardiovascular diseases.<br><br>          -  Uncontrolled or symptomatic brain metastases that are not stable or require steroids,<br>             are potentially life-threatening or have required radiation within 28 days prior to<br>             first dose of study treatment.<br><br>          -  Concomitant malignancies or previous malignancies with less than a 5-year disease-free<br>             interval at the time of first dose of study treatment; patients with adequately<br>             resected basal or squamous cell carcinoma of the skin, carcinoma in situ of the cervix<br>             or ductal carcinoma in situ may be enrolled irrespective of the time of diagnosis.<br><br>          -  Known positive serology for the human immunodeficiency virus (HIV), active hepatitis B<br>             and/or active hepatitis C.<br><br>          -  Prior randomization into this clinical study.<br><br>          -  Additional criteria exist.<br>