• Subjects ≥ 18 years at the first screening examination/visit.

• Subjects with advanced histologically or cytologically confirmed solid tumors (see below) refractory to or relapse from at least two previous therapies.

• Tumor types expected to express lower levels of FcRn relative to normal tissue including: STS, TNBC, cervical cancer, NSCLC, ovarian cancer, and KRAS mutated pancreatic ductal adenocarcinoma without requirement for testing FcRn level.

• Disease that is considered measurable by RECIST v1.1.

• Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.

• Life expectancy of at least 12 weeks.

• Human Immunodeficiency Virus (HIV)-positive trial participants should be on established antiretroviral therapy (ART) for at least four weeks and have an HIV viral load less than 400 copies/mL prior to enrollment.

• Left ventricular ejection fraction \> 50%.

• Adequate organ function: (Hb ≥10 g/dL, ANC ≥1,000/µL3, and platelets

• ≥100,000/µL3), serum bilirubin ≤.5x the institutional upper limit of normal (ULN) (unless known Gilbert's disease), Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) ≤3x ULN, and creatinine clearance \>50 mL/min as assessed by Cockcroft-Gault equation.

• For patients with known Gilbert's disease, serum unconjugated bilirubin must be \< 4 mg/dL.

• Patient must have washed out of prior chemotherapy (at least 3 weeks from last end of therapy), radiotherapy (at least 4 weeks from last end of therapy), immunotherapy (at least 4 weeks from last end of therapy), other targeted therapies (at least 4 weeks from last end of therapy), or surgery (at least 4 weeks).

• Recovery from toxicities of prior therapy. Toxicities should have recovered to CTCAE grade ≤ 1 or baseline with exception of alopecia.

• Females of reproductive potential must have had a negative pregnancy test performed within 7 days prior to the start of treatment. Additionally, female subjects of reproductive potential should agree to use effective acceptable forms of contraception: surgical sterilization (tubal ligation); total abstinence from sexual intercourse with the opposite sex; established hormonal birth control (e.g., oral, transdermal, injection, or implant) plus a barrier method or a double barrier method (intrauterine device, spermicide, or a diaphragm plus condom) for at least 1 month prior to Cycle 1 Day 1 and agreement to use such a method during study participation and for an additional 6 months after the last dose of SPEDOX-6.

• For males of reproductive potential: vasectomy or highly effective contraception (e.g., condoms, abstinence) during the study and for an additional 6 months after the last dose of SPEDOX-6.