Inclusion Criteria:

          -  Subject has locally-advanced (unresectable) or metastatic solid tumor malignancy (no
             limit to the number of prior treatment regimens) that is confirmed by available
             pathology records or current biopsy, and has received all standard therapies (unless
             the therapy is contraindicated or intolerable) felt to provide clinical benefit.

          -  Subject has an Eastern Cooperative Oncology Group (ECOG) performance status of 0, or
             1.

          -  Subject's last dose of prior antineoplastic therapy, including any immunotherapy, was
             at least 21 days prior to initiation of study drug administration. A subject with
             epidermal growth factor receptor (EGFR) or anaplastic lymphoma kinase (ALK)
             mutation-positive NSCLC is allowed to remain on EGFR tyrosine kinase inhibitor (TKI)
             or ALK inhibitor therapy until 4 days prior to the start of study drug administration.

          -  Subject has completed any radiotherapy (including stereotactic radiosurgery) at least
             14 days prior to study drug administration.

          -  Subject with metastatic castration-resistant prostate cancer (mCRPC) (positive scan
             and/or soft tissue disease documented by computed tomography/magnetic resonance
             imaging) meets both of the following:

               -  Subject has serum testosterone ≤ 50 ng/dL at screening.

               -  Subject has had an orchiectomy or plans to continue androgen deprivation therapy
                  (ADT) for the duration of study treatment.

          -  Subject has adequate organ function as indicated by laboratory values. (If a subject
             has received a recent blood transfusion, the laboratory tests must be obtained ≥ 28
             days after any blood transfusion.) Note: Growth factors, colony stimulating factors
             are not permitted in the screening period.

          -  Female subject must either:

               -  Be of non-childbearing potential: post-menopausal (defined as at least 1 year
                  without any menses for which there is no other obvious pathological or
                  physiological cause) prior to screening, or; documented surgically sterile (e.g.,
                  hysterectomy, bilateral salpingectomy, bilateral oophorectomy).

               -  Or, if of childbearing potential: Agree not to try to become pregnant during the
                  study treatment and for 6 months after the final study drug administration; and
                  have a negative urine or serum pregnancy test prior to study drug administration;
                  and if heterosexually active, agree to consistently use 1 form of highly
                  effective birth control starting at screening and throughout the study treatment
                  and 6 months after the final study drug administration.

          -  Female subject must agree not to breastfeed starting at screening and throughout the
             study treatment, and for 6 months after the final study drug administration.

          -  Female subject must not donate ova starting at screening and throughout the study
             treatment, and for 6 months after the final study drug administration.

          -  A sexually active male subject with female partner(s) who are of childbearing
             potential is eligible if :

               -  The male subject agrees to use a male condom starting at screening and continues
                  throughout the study treatment, and for 6 months after the final study drug
                  administration.

               -  The male subject has not had a vasectomy or is not sterile, as defined below and
                  the subject's female partner(s) is utilizing 1 form of highly effective birth
                  control starting at screening and continuing throughout the study treatment and
                  for 6 months after the final study drug administration.

          -  Male subject must not donate sperm starting at screening and throughout the study
             treatment, and for 6 months after the final study drug administration.

          -  Male subject with a pregnant or breastfeeding partner(s) must agree to remain
             abstinent or use a condom for the duration of the pregnancy or time partner is
             breastfeeding throughout the study treatment and for 6 months after the final study
             drug administration.

          -  Subject agrees not to participate in another interventional study while receiving
             study drug (subjects who are currently in the follow-up period of an interventional
             clinical trial are allowed).

        Additional Inclusion Criteria for Subjects in the Expansion Cohorts:

          -  Subject has at least 1 measureable lesion per RECIST 1.1. The measureable lesion must
             be outside the field of radiation if subject had prior radiotherapy. Lesions situated
             in a previously irradiated area are considered measurable if progression has been
             demonstrated in such lesions. Subjects with mCRPC who do not have measurable lesions
             must have at least 1 of the following:

               -  Progression with 2 or more new bone lesions, or

               -  Prostate specific antigen (PSA) progression (defined as a minimum of 3 rising PSA
                  levels with an interval of ≥ 1 week between each determination) within 6 weeks
                  prior to study drug administration and a PSA value at the screening visit ≥ 2
                  ng/mL.

          -  Subject consents to provide available tumor specimen in a tissue block or unstained
             serial slides obtained within 8 to 56 days prior to first dose of study treatment.
             Note: This does not apply to subjects with mCRPC who do not have measurable disease.

          -  Subject is an appropriate candidate for tumor biopsy and consents to undergoing a
             tumor biopsy (core needle biopsy or excision) during the treatment period. Note: This
             does not apply to subjects with mCRPC who do not have measurable disease.

          -  Subject meets one of the following:

               -  Subject has the tumor type for which a confirmed response was observed in a
                  monotherapy or in combination with nivolumab dose escalation or RP2D cohort; or

               -  ASP1948 monotherapy or in combination with pembrolizumab expansion cohort is
                  opened due to achieving predicted efficacious exposure, subject has squamous cell
                  carcinoma of the head and neck (SCCHN); or

               -  RP2D monotherapy cohort is opened and subject has NSCLC, mCRPC, ovarian cancer,
                  pancreatic cancer or breast cancer; or • o RP2D combination with pembrolizumab
                  expansion cohort, is opened and subject has NSCLC (all PD-L1 status), NSCLC PD-L1
                  high*, ovarian cancer, colorectal cancer, or breast cancer.

                    -  NSCLC with PD-L1 high expressing tumor as determined by immunohistochemistry
                       at a central laboratory during the screening period.

        Additional Inclusion Criteria for Re-treatment:

        Subjects may be eligible for study drug re-treatment if the study remains open and the
        subject continues to meet all of the eligibility criteria above (except prior use of this
        drug) and the following conditions:

          -  Subject stopped initial treatment with ASP1948 or ASP1948 in combination with
             nivolumab or pembrolizumab after attaining a confirmed CR or PR or SD.

          -  Subject experienced a confirmed disease progression by iRECIST (iCPD) after stopping
             their initial treatment with ASP1948 or ASP1948 in combination with nivolumab or
             pembrolizumab.

          -  Subject did not receive any prohibited anti-cancer treatment since the last dose of
             ASP1948 or ASP1948 in combination with nivolumab or pembrolizumab.

          -  Subject did not experience a toxicity that met the discontinuation criteria during the
             initial treatment with ASP1948 or ASP1948 in combination with nivolumab or
             pembrolizumab.

        Exclusion Criteria:

          -  Subject weighs < 45 kg.

          -  Subject has received investigational therapy (other than an investigational epidermal
             growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) in a subject with EGFR
             mutations or ALK inhibitor in a subject with an ALK mutation) within 21 days prior to
             start of study drug.

          -  Subject requires or has received systemic steroid therapy or any other
             immunosuppressive therapy within 14 days prior to study drug administration. Subjects
             using a physiologic replacement dose of hydrocortisone or its equivalent(defined as up
             to 30 mg per day of hydrocortisone, 2 mg per day of dexamethasone or up to 10 mg per
             day of prednisone) are allowed. Note: Corticosteroids for prophylaxis (e.g., contrast
             dye allergy) or for brief treatment of conditions not related to study treatment
             (e.g., delayed-type hypersensitivity reaction caused by a contact allergen) is also
             allowed.

          -  Subject has symptomatic central nervous system (CNS) metastases or subject has
             evidence of unstable CNS metastases even if asymptomatic (e.g., progression on scans).
             Subjects with previously treated CNS metastases are eligible, if the subject is
             clinically stable and has no evidence of CNS progression by imaging for at least 28
             days prior to start of study treatment and are not requiring immunosuppressive doses
             of systemic steroids (> 30 mg per day of hydrocortisone, > 2 mg per day of
             dexamethasone or > 10 mg per day of prednisone or equivalent) for longer than 14 days.

          -  Subject has leptomeningeal disease as a manifestation of the current malignancy.

          -  Subject has an active autoimmune disease that has required systemic treatment in the
             past 2 years. Subjects with type 1 diabetes mellitus, stable endocrinopathies
             maintained on appropriate replacement therapy and skin disorders (e.g., vitiligo,
             psoriasis or alopecia) not requiring systemic treatment are allowed.

          -  Subject was discontinued from prior immunomodulatory therapy due to a Grade ≥ 3
             toxicity that was mechanistically related (e.g., immune related) to the agent.

          -  Subject has known history of serious hypersensitivity reaction to a known ingredient
             of ASP1948, nivolumab or pembrolizumab or severe hypersensitivity reaction to
             treatment with another monoclonal antibody.

          -  Subject with positive Hepatitis B virus antibodies and surface antigen (indicating
             acute Hepatitis B virus (HBV) or chronic HBV) or Hepatitis C (HCV ribonucleic acid
             (RNA) (qualitative)). Hepatitis C RNA testing is not required in subjects with
             negative Hepatitis C antibody testing. Hepatitis B virus antibodies are not required
             in subjects with negative Hepatitis B surface antigen.

          -  Subject has received a live vaccine against infectious diseases within 28 days prior
             to initiation of study treatment.

          -  Subject has a history of drug-induced pneumonitis (interstitial lung disease), a
             history of (non-infectious) pneumonitis that required steroids, radiation pneumonitis
             or currently has pneumonitis.

          -  Subject has an active infection requiring systemic therapy within 14 days prior to
             study drug treatment.

          -  Subject is expected to require another form of antineoplastic therapy while on study
             treatment.

          -  Subject has an uncontrolled intercurrent illness including, but not limited to cardiac
             arrhythmia or psychiatric illness/social situations that would limit compliance with
             study requirements.

          -  Subject's AEs (excluding alopecia) from prior therapy have not improved to Grade 1 or
             baseline within 14 days prior to start of study treatment.

          -  Subject has significant cardiovascular disease including:

               -  Subject has inadequately controlled hypertension (defined as systolic blood
                  pressure > 150 and/or diastolic blood pressure > 100 mmHg on antihypertensive
                  medications).

               -  Subject has a history of myocardial infarction or unstable angina within 6 months
                  prior to day 1.

               -  Subject has New York Heart Association Class II or greater chronic heart failure
                  (CHF).

               -  History of cerebrovascular accident (CVA) or transient ischemic attack (TIA)
                  within 6 months prior to study treatment.

               -  Subject has significant vascular disease (e.g., aortic aneurysm requiring
                  surgical repair or recent peripheral arterial thrombosis) within 6 months prior
                  to study treatment.

          -  Subject has a history of hemoptysis (bright red blood of ½ teaspoon or more per
             episode) within 12 weeks prior to study treatment.

          -  Subject has evidence of a bleeding diathesis or significant coagulopathy.

          -  Subject has inadequate recovery from prior surgical procedure or has had a major
             surgical procedure, open biopsy or significant traumatic injury within 28 days prior
             to day 1, or anticipates the need for a major surgical procedure during the course of
             the study or minor surgery within 7 days of starting study treatment.

          -  Subject has initiated new treatment with medications that affect the coagulation
             cascade with an international normalized ratio (INR) ≥ 2 such as vitamin K
             antagonists, heparins and direct thrombin inhibitors or the use of factor Xa
             inhibitors within 28 days prior to the start of study treatment. Note: If the subject
             started receiving such medications more than 28 days prior to the start of study
             treatment and needs to continue, this is allowed. However, new anticoagulation may not
             be initiated within 28 days prior to the start of study treatment.

          -  Subject has any condition that makes the subject unsuitable for study participation.

          -  Subject has a known history of human immunodeficiency virus (HIV) infection. No HIV
             testing is required unless mandated by local health authority.

          -  Subject has had an allogeneic tissue solid organ transplant.

          -  Subject has known history of COVID-19 positive polymerase chain reaction (PCR) test
             within 4 weeks prior to start of study treatment.

        Additional Exclusion Criteria for Subjects in Expansion Cohorts:

          -  Subject has a prior malignancy active (i.e., requiring treatment or intervention)
             within the previous 2 years, except for locally curable malignancies that have been
             apparently cured, which are allowed, such as basal or squamous cell skin cancer,
             superficial bladder cancer or carcinoma in situ of the cervix or breast.

          -  Subject has received prior treatment with a neuropilin-1 (NRP1) inhibitor.

        Additional Exclusion Criteria for Re-treatment:

          -  Subjects who have completed 40 weeks (ASP1948 monotherapy or combination therapy with
             nivolumab cohorts) or 57 weeks (ASP1948 combination therapy with pembrolizumab) of
             follow-up with disease control are not eligible for retreatment.

          -  Subject currently has an ongoing Adverse Event (AE) related to the initial ASP1948 or
             ASP1948 in combination with nivolumab or pembrolizumab treatment that meets the
             criteria for treatment interruption or discontinuation.