Inclusion Criteria:  Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 2 Adequate organ function (bone marrow, hepatic, renal, cardiovascular) Left ventricular ejection fraction of ≥ 50% Female patients of childbearing potential must have a negative pregnancy test within 7 days of the start of treatment and must agree to use a highly effective method of contraception during the trial Patients must have recovered from the effects of any prior cancer related therapy, radiotherapy or surgery (toxicity ≤ Grade 1) All patients on prior investigational agents must wait at least 5 half-lives of the agent in question, or 28 days, whichever is longer before study entry  Most recent lab values meet the following criteria:  Absolute neutrophil count > 1.0 x 10^3/μL; Platelet count > 75,000/μL; Hemoglobin > 9.0 g/dL  Histologically confirmed advanced or metastatic solid tumor indicated below that is relapsed, refractory, or intolerant to available therapies with known benefit:  Sarcoma not amendable to curative treatment with surgery or radiotherapy; Melanoma (non-resectable or metastatic); Small cell lung cancer (extensive-stage); Non-small cell lung cancer; Triple negative breast cancer (histopathologically or cytologically confirmed). Esophageal cancer Cervical cancer Head and neck cancer  Exclusion Criteria:  Known hypersensitivity to any of the components of PRT1419 Primary malignancies of the CNS, or uncontrolled CNS metastases, including impending spinal cord compression Female patients who are pregnant or lactating Inflammatory disorders of the gastrointestinal tract, or subjects with GI malabsorption Mean QTcF interval of >480 msec History of heart failure, additional risk factors for arrhythmias or requiring concomitant medications that prolong the QT/QTc interval HIV positive; known active hepatitis B or C Uncontrolled intercurrent illnesses Treatment with strong inhibitors of CYP2C8 Prior exposure to an MCL1 inhibitor  History of another malignancy except:  Malignancy treated with curative intent with no known active disease for >2 years at study entry; Adequately treated non-melanoma skin cancer or lentigo maligna without evidence of disease; Adequately treated carcinoma in situ without evidence of disease; Other concurrent low-grade malignancies (i.e chronic lymphocytic leukemia (Rai 0)) may be considered after consultation with Sponsor.