Inclusion Criteria:

          -  The patient must have histologic or cytologic evidence of a malignant solid tumor and
             must have disease that is resistant to or relapsed following available standard
             systemic therapy, or for which there is no standard systemic therapy or reasonable
             therapy likely to result in clinical benefit.

          -  The patient must have advanced disease, defined as cancer that is either metastatic,
             OR locally advanced and unresectable (and for which additional radiation therapy or
             other locoregional therapies are not considered feasible).

          -  The patient must have disease that is measurable by standard imaging techniques, per
             the Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST 1.1), or
             evaluable per RECIST 1.1. (For patients with prior radiation therapy, measurable
             lesions must be outside of any prior radiation field[s], unless disease progression
             has been documented at that disease site subsequent to radiation.)

          -  The patient is ≥18 years old.

          -  The patient has an ECOG PS of 0-2.

          -  The patient has adequate baseline organ function, as demonstrated by the following:

               -  Serum creatinine ≤1.5 × institutional upper limit of normal (ULN) or calculated
                  creatinine clearance >30 mL/min.

               -  Serum albumin ≥2.5 g/dL.

               -  Bilirubin ≤1.5 × institutional ULN.

               -  Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤2.5 ×
                  institutional ULN (patients with hepatic metastases must have AST/ALT ≤5 times
                  ULN).

               -  International normalized ratio (INR) ≤1.5 or prothrombin time (PT) ≤1.5 × ULN;
                  and either partial thromboplastin time or activated partial thromboplastin time
                  (PTT or aPTT) ≤1.5 × ULN.

          -  The patient has adequate baseline hematologic function, as demonstrated by the
             following:

               -  Absolute neutrophil count (ANC) ≥1.5×10⁹/L

               -  Hemoglobin ≥8 g/dL, with no red blood cell (RBC) transfusions within the prior 14
                  days.

               -  Platelet count ≥100×10⁹/L, with no platelet transfusions within the prior 14
                  days.

          -  If the patient is a woman of child bearing potential (WOCBP), she has had a negative
             serum or urine pregnancy test within 1 week prior to treatment.

          -  The patient (male and female) agrees to use acceptable contraceptive methods for the
             duration of time on the study, and continue to use acceptable contraceptive methods
             for 1 month after the last dose of SL-801.

          -  The patient has signed informed consent prior to initiation of any study-specific
             procedures or treatment.

          -  The patient is able to adhere to the study visit schedule and other protocol
             requirements, including follow-up for survival assessment.

        Exclusion Criteria:

          -  The patient has persistent clinically significant ≥Grade 2 toxicities from previous
             anticancer therapy (excluding Grade 2 chemotherapy-related neuropathy which is
             permitted, and excluding Grade 2-3 laboratory abnormalities if they are not associated
             with symptoms, are not considered clinically significant by the Investigator, and can
             be managed with available medical therapies).

          -  The patient has received treatment with chemotherapy, external-beam radiation, or
             other systemic anticancer therapy within 28 days prior to study entry (Patients with
             advanced prostate cancer who are receiving luteinizing hormone releasing hormone
             [LHRH] agonists are permitted onto the study and should continue use of these agents
             during study treatment).

          -  The patient has received treatment with an investigational systemic anticancer agent
             within 28 days prior to C1D1.

          -  The patient has previously received treatment with SL-801 or another investigational
             agent that inhibits the XPO1/CRM1 pathway.

          -  The patient has an additional active malignancy that may confound the assessment of
             the study endpoints. Patients with a past cancer history (active malignancy within 2
             years prior to study entry) with substantial potential for recurrence must be
             discussed with the Sponsor before study entry. Patients with the following concomitant
             neoplastic diagnoses are eligible: non-melanoma skin cancer, carcinoma in situ
             (including transitional cell carcinoma, cervical intraepithelial neoplasia),
             organ-confined prostate cancer with no evidence of progressive disease.

          -  The patient has clinically significant cardiovascular disease (e.g., uncontrolled or
             any New York Heart Association Class 3 or 4 congestive heart failure [Appendix 1],
             uncontrolled angina, history of myocardial infarction, unstable angina or stroke
             within 6 months prior to study entry, uncontrolled hypertension or clinically
             significant arrhythmias not controlled by medication).

          -  The patient has uncontrolled, clinically significant pulmonary disease (e.g., chronic
             obstructive pulmonary disease, pulmonary hypertension) that, in the Investigator's
             opinion, would put the patient at significant risk for pulmonary complications during
             the study.

          -  The patient has known active or suspected brain or leptomeningeal metastases. (Central
             nervous system [CNS] imaging is not required prior to study entry unless there is a
             clinical suspicion of CNS involvement). Patients with stable, treated brain metastases
             are eligible provided there is no evidence of CNS disease growth on imaging for at
             least 3 months following radiation therapy or other locoregional ablative therapy to
             the CNS.

          -  The patient is receiving immunosuppressive therapy for prophylaxis following a prior
             organ transplant (solid organ or allogeneic stem cell) or management of
             immune-mediated toxicities due to immunotherapy. Low-dose corticosteroid (defined as <
             10mg/day of prednisone or equivalent) therapy is permitted.

          -  The patient has uncontrolled intercurrent illness including, but not limited to,
             uncontrolled infection, disseminated intravascular coagulation, or psychiatric
             illness/social situations that would limit compliance with study requirements.

          -  The patient is pregnant or breast feeding.

          -  The patient has known positive status for human immunodeficiency virus active or
             chronic Hepatitis B or Hepatitis C.

          -  The patient is oxygen-dependent.

          -  The patient has any medical condition which in the opinion of the Investigator places
             the patient at an unacceptably high risk for toxicities.