Inclusion Criteria:

          1. Signed informed consent

          2. Age ≥ 18 years

          3. ECOG Performance Status ≤ 2

          4. [Part 1 - Dose Escalation] Histologically or cytologically diagnosed metastatic breast
             cancer that has progressed on or after standard of care therapy and for which no
             standard of care therapy is available that would confer clinical benefit

          5. [Part 2 - Dose Expansion] Histologically or cytologically diagnosed metastatic
             triple-negative breast cancer with <1% expression of ER and PR and negative for HER2
             (either 0 or 1+ by IHC or IHC 2+ and fluorescence in situ hybridization (FISH)
             negative) from the time of initial diagnosis that has progressed on or after standard
             of care therapy and for which no standard of care therapy is available that would
             confer clinical benefit

          6. [Part 1 - Dose Escalation] Evaluable or measurable disease by RECISTv1.1

          7. [Part 2 - Dose Expansion] Measurable disease by RECISTv1.1

          8. Adequate laboratory parameters including:

               1. Absolute Neutrophil Count (ANC) ≥ 1500/mm^3

               2. Platelets ≥ 100,000/mm^3

               3. AST/SGOT ≤ 2.5 x ULN (≤ 5 x ULN if known liver involvement)

               4. ALT/SGPT ≤ 2.5 x ULN (≤ 5 x ULN if known liver involvement)

               5. Total bilirubin ≤ 1.5 x ULN (unless diagnosis of Gilbert's syndrome in which case
                  < 3.0 times ULN)

               6. Serum creatinine ≤ 1.5 x ULN or estimated GFR ≥ 60 mL/min

          9. If residual treatment related toxicity from prior therapy:

               1. Treatment related toxicity resolved to at least Grade 1 (alopecia excepted), or

               2. Treatment related toxicity resolved to at least Grade 2 with prior approval of
                  the Medical Monitor

         10. Available archival or fresh tumor tissue (Formalin-fixed paraffin-embedded [FFPE])

         11. [Females] The patient must be postmenopausal, surgically sterile, or agree to use
             adequate contraception (adequate as determined by the PI - may include abstinence)
             throughout the study and for a least 30 days following the last dose of PMD-026

         12. [Males] The patient must be surgically sterile or must agree to use adequate
             contraception (adequate as determined by the PI - may include abstinence) throughout
             the study and for at least 30 days following the last dose of PMD-026

         13. [Males] The patient must agree to refrain from donating sperm throughout the study and
             for at least 30 days following the last dose of PMD-026

         14. [Females] If of childbearing potential, the patient must have a negative serum
             pregnancy test

        Exclusion Criteria:

          1. ≤ 14 days from prior chemotherapy, biological or investigational therapy

          2. Use of any medications known to result in a prolongation of the QT/QTc interval

          3. Use of any medication that is a strong inducer or substrate of cytochrome P450 3A

          4. Use of any medications that is a substrate of BCRP

          5. Use of any medication that is a substrate of MATE2K

          6. ≤ 28 days from prior irradiation (including therapeutic radioisotopes such as
             strontium 89)

          7. ≤ 7 days from limited field irradiation for palliation

          8. ≤ 28 days from major surgical procedures

          9. ≤ 7 days from minor surgical procedures (no waiting period required following central
             catheter placement)

         10. Central nervous system metastases, unless appropriately treated and neurologically
             stable for ≥ 28 days

         11. Known history of leptomeningeal metastases

         12. Uncontrolled bacterial, viral, or fungal infection (s) requiring systemic therapy

         13. Pregnant or currently breast-feeding

         14. Known Hepatitis B or Hepatitis C infection

         15. Known HIV-positive with CD4+ cell counts < 350 cells/uL

         16. Known HIV-positive with a history of an AIDS-defining opportunistic infection

         17. History of clinically significant cardiovascular abnormalities including:

               1. Congestive heart failure (NYHA classification ≥ 3 in within 6 months of first
                  dose of PMD-026

               2. Unstable angina pectoris

               3. Myocardial infarction within 12 months of study entry

               4. Arrhythmias requiring continued treatment (controlled atrial fibrillation
                  allowed)

               5. QTcF interval > 460 msec (using Fridericia's formula)

         18. Presence of active gastrointestinal disease or other condition that is expected to
             interfere significantly with the absorption, distribution, metabolism, or excretion of
             oral therapy (e.g. ulcerative disease, uncontrolled nausea, vomiting, diarrhea Grade ≥
             2, and malabsorption syndrome)

         19. Inadequately controlled hypertension defined as systolic blood pressure >180 mmHg or
             diastolic blood pressure >100 mmHg (patients with values above these levels must have
             their blood pressure controlled prior to starting treatment)

         20. Serious active infection at the time of treatment, or another serious underlying
             medical condition that would impair the ability of the patient to receive protocol
             treatment

         21. Other known active cancer(s) likely to require treatment in the next year that would
             impact the assessment of any study endpoints

         22. Psychological, familial, sociological, or geographical conditions that do not permit
             compliance with the protocol