Controlled Study of Rigosertib Versus Physician's Choice of Treatment in MDS Patients After Failure of an HMA

This is a Phase III, open-label, randomized, controlled, international study. Approximately
360 patients < 82 years of age with MDS classified as RAEB-1, RAEB-2, or RAEB-t who received
AZA or DAC for ≤ 9 months and/or ≤ 9 cycles over 12 months and had their last dose of AZA or
DAC within 6 months prior to screening will be stratified by:

- Very high risk (VHR) vs non-VHR per IPSS-R, and

- Geographic region (North America vs Europe vs Asia; because approved products and
standard of care may vary by region), and randomly assigned in a 2:1 ratio to one of the
following 2 treatment groups:

- Rigosertib 1800 mg/24 hr administered as a 72 hr CIV infusion on Days 1, 2, and 3 of a 2
week cycle for the first 8 cycles, and on Days 1, 2, and 3 of a 4-week cycle thereafter
(N = approximately 240 patients);

- Physician's Choice of alternative treatment, which may include any approved or
standard-of-care therapy that the patient has not shown to be hypersensitive to, based
on frequently used treatment for MDS, as per institutional guidelines, after receipt of
HMAs (N = approximately 120 patients). The drugs used in the Physician's Choice arm
should be used according to the recommendations, if clinically appropriate, provided in
the corresponding Summary of Product Characteristics (SmPC) and Prescribing Information
of these drugs. Experimental therapies are not allowed on the PC arm.

Patients will be treated until 2006 IWG progression criteria are met (ie, 50% increase of BM
blasts or worsening of cytopenias) or until an unacceptable toxicity or intolerance.

For all randomized patients who discontinue study treatment, subsequent therapies with their
start and end dates, as well as survival time after treatment discontinuation, will be
documented at least monthly until death.

Patients in the PC group who progress will not be allowed to cross over to rigosertib.

All patients in both treatment groups will be allowed, as medically justified, access to RBC
and platelet transfusions and to growth factors (granulocyte colony-stimulating factor
(G-CSF), erythropoietin, and thrombopoietin).

Inclusion Criteria:

- MDS classified as follows:

- RAEB-1 per World Health Organization (WHO) MDS criteria (5% to <10% BM blasts)

- RAEB-2 per WHO MDS criteria (10% to <20% BM blasts)

- RAEB-t per French-American-British (FAB) classification (20% to 30% BM blasts)

- At least one cytopenia (ANC < 1800/µL or platelet count < 100,000/µL or hemoglobin
[Hgb] < 10 g/dL)

- Progression (according to 2006 IWG criteria) at any time after initiation of AZA or
DAC treatment or Failure to achieve complete or partial response or hematological
improvement (HI) (according to 2006 IWG) after at least six 4-week cycles of AZA or
either four 4-week or four 6-week cycles of DAC administered or Relapse after initial
complete or partial response or HI (according to 2006 IWG criteria)

- Duration of prior HMA therapy ≤ 9 months and/or total ≤ 9 cycles of prior HMA therapy
in ≤ 12 months

- Last dose of AZA or DAC within 6 months before the planned date of randomization;
however, must be off these treatments for ≥ 4 weeks before randomization

- Has failed to respond to, relapsed following, not eligible for, or opted not to
participate in allogeneic stem cell transplantation

- Off all treatments for MDS (including AZA and DAC) for ≥ 4 weeks before randomization;
growth factors (G-CSF, erythropoietin and thrombopoietin) and transfusions are allowed
before and during the study as clinically indicated

- Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2

- Willing to adhere to protocol prohibitions and restrictions

- Patient must sign informed consent form to indicate patient's understanding study's
purpose and procedures and willingness to participate. Should patient be incapable of
giving consent, the patient's legally authorized representative (as defined by local
regulation) must give consent. However, should patient, in any manner, choose not to
participate this takes precedence and will be respected.

- Patients with 5q- syndrome should have failed to respond to or progressed on treatment
with lenalidomide, where available and indicated

Exclusion Criteria:

- Previous participation in a clinical study of IV or oral rigosertib; patients who
failed screening for other rigosertib studies may be screened for participation

- Eligible to receive induction chemotherapy, such as 7-10 days of cytosine arabinoside
plus 2-3 days of an anthracycline, or high-dose cytarabine

- Suitable candidate to receive allogeneic stem cell transplantation; patient is
eligible for study if a suitable candidate refuses to undergo an allogeneic stem cell
transplant or a suitable donor cannot be found

- Any active malignancy within the past year, except basal cell or squamous cell skin
cancer or carcinoma in situ that is unlikely to progress in two years

- Uncontrolled intercurrent illness including, but not limited to, symptomatic
congestive heart failure or unstable angina pectoris

- Active infection not adequately responding to appropriate therapy

- Total bilirubin ≥1.5 mg/dL not related to hemolysis or Gilbert's disease

- Alanine transaminase (ALT)/aspartate transaminase (AST) ≥2.5 x upper limit of normal
(ULN)

- Serum creatinine ≥2.0 mg/dL or eGFR (estimated Glomerular Filtration Rate) < 40
mL/min.

- Known active HIV, hepatitis B or hepatitis C, where active is defined as follows:

- HIV or hepatitis C - presence of viral load

- Hepatitis B - antigen positive

- Uncorrected hyponatremia (defined as serum sodium value of <130 mEq/L)

- Female patients of child-bearing potential and male patients with sexual partners of
child-bearing potential who are unwilling to follow strict contraception requirements
before entry and throughout the study, up to and including the 30-day non-treatment
follow-up period. Examples of acceptable contraception methods include:

- estrogen-gestagen based contraceptives associated with inhibition of ovulation
(oral, intravaginal, transdermal),

- gestagen-only based contraceptives associated with inhibition of ovulation (oral,
injectable, implantable),

- intra-uterine devices (IUDs),

- intra-uterine hormone-releasing systems (IUSs),

- bilateral tubal occlusion

- vasectomized partner

- sexual abstinence in accordance with an individual's lifestyle

- Female patients of child-bearing potential (pre-menopausal and not surgically
sterilized) who are breast-feeding or have a positive blood beta-human chorionic
gonadotropin pregnancy test at Screening

- Major surgery without full recovery or within 3 weeks before planned randomization;

- Uncontrolled hypertension

- New onset seizures (within 3 months before planned randomization) or poorly controlled
seizures

- Any other concurrent investigational agent or chemotherapy, radiotherapy,
immunotherapy, or corticosteroids (prednisone up to 20 mg/day or its equivalent is
permitted for chronic conditions)

- Treatment with cytarabine at any dose, lenalidomide, or any other therapy targeted to
the treatment of MDS (other than growth factors and other supportive care measures)
within 4 weeks of planned randomization

- Investigational therapy within 4 weeks of planned randomization

- Psychiatric illness or social situation that would limit the patient's ability to
tolerate and/or comply with study requirements.

- Patient previously diagnosed with AML (defined as a bone marrow or peripheral blood
blast percentage of >30%).