Inclusion Criteria:

        Patients enrolled in Part A must receive the 99mTc- etarfolatide scan but they do not need
        to have FR-positive target lesions.

        Parts A and B:

        To qualify for enrollment, the following criteria must be met:

          1. Patient must have the ability to understand and sign an approved informed consent form
             (ICF).

          2. Patient must be ≥ 18 years of age.

          3. Patient must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0
             or 1.

          4. Patient must have a life expectancy of > 3 months.

          5. Patient must have at least one measurable lesion per RECIST v1.1 Criteria as assessed
             on baseline radiologic evaluation obtained no more than 28 days prior to beginning
             study therapy.

          6. Patients with central nervous system (CNS) metastases that are symptomatic must have
             received therapy (e.g., surgery, XRT, gamma knife, etc.) and be neurologically stable
             and off of steroids. The patient should be off steroids at least 14 days before
             registration. Patients with asymptomatic CNS metastatic disease without associated
             edema, shift, and a requirement for steroids or anti-seizure medications may be
             eligible after discussion with the sponsor medical monitor.

          7. Patients must have formalin fixed tissue (biopsy or FNA) available.

          8. Patient must have recovered (to baseline/stabilization) from prior chemo or radio
             therapy and associated acute toxicities must have resolved to a NCI CTCAE V4 Grade 1
             or less, with the exception of alopecia.

          9. Patients treated with prior radiation therapy may be eligible if:

               1. Radiotherapy was completed at least 2 weeks before first dose of EC1456 and

               2. Patient has recovered from acute radiation toxicity.

         10. Patients must have adequate organ function:

               1. Bone marrow reserve: Absolute neutrophil count (ANC) ≥ 1.5 x 109/L; Platelets ≥
                  100 x 109/L; Hemoglobin ≥ 9 g/dL.

               2. Cardiac:

             i. QTcFridericia (QTcF) < 450 msec on at least 2 of 3 screening ECG's. On site
             determination of QTcF may be used for screening purposes.

             ii. Left ventricular ejection fraction (LVEF) equal to or greater than the
             institutional lower limit of normal. LVEF must be evaluated within 28 days prior to
             C1D1.

             iii. Cardiac Troponin I or T within normal limit. (whichever troponin is done for
             screening will need to be done throughout the rest of the study).

             c. Hepatic: Total bilirubin ≤ 1.5 x the upper limit of normal (ULN); Alanine
             aminotransferase (ALT), aspartate aminotransferase (AST) ≤ 3.0 x ULN OR ≤ 5.0 x ULN
             for patients with liver metastases.

             d. Renal: Serum creatinine ≤ 1.5 x ULN or for patients with serum creatinine > 1.5
             ULN, creatinine clearance ≥ 50 mL/min.

             Patients of childbearing potential:

         11. All women of childbearing potential MUST have a negative urine or serum pregnancy test
             within 1 week prior to the 99mTc-etarfolatide imaging procedure and within 1 week
             prior to treatment with EC1456.

         12. Women of child bearing potential must practice an effective method of birth control
             (i.e., oral, transdermal or injectable contraceptives, intrauterine device [IUD], or
             double-barrier contraception, such as diaphragm and spermicidal jelly) for the
             duration of their participation in the trial through 90 days following the last dose
             of EC1456.

         13. Male patients who are sexually active must practice an effective method of birth
             control (e.g., condom and spermicidal jelly) for the duration of their participation
             in the trial through 90 days following the last dose of EC1456.

             Patient and Disease Specific Inclusion Criteria: Part A

             EC1456 dose escalation cohorts (Treatments 1, 2, 3, and 4):

         14. Patients must have pathologically confirmed metastatic or locally advanced solid
             cancer (preferably TNBC, NSCLC, ovarian, or endometrial cancers due to frequent high
             FR expression in these cancers) that has failed to respond to standard therapy, is not
             amenable to standard therapy, or for which standard therapy does not exist.

         15. TNBC and ovarian patients must agree to submit results of BRCA 1/2 status (i.e.,
             deleterious mutation present, mutation of unknown significance, no mutation detected)
             if known. BRCA testing is not required for study inclusion.

         16. Patients must have received ≤ 4 prior lines of systemic anti-cancer therapy (including
             but not limited to cytotoxic agents, targeted inhibitors, and monoclonal antibodies).
             Hormonal therapies are not included toward this criterion.

         17. Patients must undergo a 99mTc-etarfolatide SPECT imaging procedure in compliance with
             the Investigator's Imaging Operations Manual (IIOM). FR expression on 99mTc
             -etarfolatide SPECT is not required for inclusion in Treatments 1, 2, 3, and 4.

             (Patients who underwent a 99mTc-etarfolatide SPECT/CT imaging procedure as a subject
             on Endocyte study EC20.12 will not be required to have a repeat scan for participation
             in study EC1456-01 if the scan was obtained within 4 weeks of cycle 1 day 1 of EC1456
             administration and has been deemed acceptable by Endocyte Imaging.)

             Part B Only:

             Patient and Disease Specific Inclusion Criteria: Part B

             Patients with FR-positive NSCLC (all subtypes): (Treatments 5, 6, and 7)

         18. Patients with NSCLC (all subtypes) must have received one prior platinum based therapy
             for advanced or metastatic disease. No additional cytotoxic therapy for advanced or
             metastatic disease is allowed. Any number of prior targeted therapies (e.g.,
             inhibitors of ALK, EGFR, and PD-1 or PD-L1) are allowed. Patients with known relevant
             genomic tumor aberrations (i.e., EGFR, ALK, ROS-1, etc) must have received and
             progressed on approved therapy for these aberrations. This information must be
             documented prior to study entry.

         19. Patients must undergo a 99mTc-etarfolatide SPECT imaging procedure in compliance with
             the Investigator's Imaging Operations Manual (IIOM) and be FR-positive.

        Exclusion Criteria:

        Parts A and B:

        The presence of any of the following will exclude patients from the study:

          1. Systemic anti-cancer treatment, except hormonal treatment, within 28 days prior to
             EC1456 administration unless there are no remaining or ongoing uncontrolled
             toxicities. Please contact the medical monitor to discuss requests for less than 28
             day washout period.

          2. Known hypersensitivity to the components of the study therapy or its analogs.

          3. Carcinomatous meningitis and/or symptomatic central nervous system (CNS) metastases.

          4. Malignancies that are expected to alter life expectancy or may interfere with disease
             assessment. Patients with adequately treated non-melanoma skin cancer, carcinoma in
             situ of the cervix, or low-grade (Gleason score ≤ 6) localized prostate cancer, ductal
             carcinoma in situ (DCIS), and patients with prior history of malignancy who have been
             disease free for more than 3 years are eligible.

          5. Serious cardiac illness or medical conditions such as unstable angina, pulmonary
             embolism, or uncontrolled hypertension.

          6. Patients considered at risk for life-threatening QTc prolongation (i.e., personal or
             family history of Long QT syndrome, presence of implantable pacemaker or implantable
             cardioverter defibrillator, etc.).

          7. Use of the following medications within 6 months prior to EC1456 administration:
             amiodarone, disopyramide, dofetilide, dronedarone, flecanamide, ibutilide, quinidine,
             or sotalol.

          8. Need for concurrent anti-folate therapy such as methotrexate for rheumatoid arthritis.

          9. Other concurrent chemotherapy, immunotherapy, radiotherapy, or investigational
             therapy.

         10. Pregnant or lactating women.

         11. Active uncontrolled infections.

         12. Known active Hepatitis B or C infection.

         13. Unable or unwilling to have a pretreatment scan performed with 99mTc-etarfolatide for
             any reason (such as claustrophobia, an inability to lie supine on an imaging table
             because of pain or cardiopulmonary disease, etc.).