Inclusion Criteria:

          -  DOSE ESCALATION COHORTS: Patients must have a biopsy-proven solid tumor that is
             metastatic or unresectable and has progressed on at least one line of standard therapy

          -  DOSE EXPANSION COHORTS: Patients must have biopsy proven metastatic or unresectable
             small cell lung cancer (SCLC), poorly differentiated neuroendocrine carcinoma (PD-NEC)
             (any extrapulmonary neuroendocrine carcinoma with small cell or large cell histology)
             or pancreatic adenocarcinoma (PDA) and have progressed on at least one line of
             standard therapy

          -  DOSE EXPANSION COHORTS: Patients must have at least one measurable lesion outside of
             the lesion to be biopsied

          -  Patients must be able to swallow pills

          -  Eastern Cooperative Oncology Group (ECOG) performance status =< 2 (Karnofsky >= 60%)

          -  Hemoglobin > 9 g/dL

          -  Leukocytes >= 3,000/mcL

          -  Absolute neutrophil count >= 1,500/mcL

          -  Platelets >= 100,000/mcL

          -  Total bilirubin =< 2 x institutional upper limit of normal (ULN)

          -  Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase
             [SGOT])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT])
             =< 3 x institutional ULN

          -  Glomerular filtration rate (GFR) >= 60 mL/min/1.73 m^2

          -  Human immunodeficiency virus (HIV)-infected patients on effective anti-retroviral
             therapy with undetectable viral load within 6 months are eligible for this trial

          -  For patients with evidence of chronic hepatitis B virus (HBV) infection, the HBV viral
             load must be undetectable on suppressive therapy, if indicated

          -  Patients with a history of hepatitis C virus (HCV) infection must have been treated
             and cured. For patients with HCV infection who are currently on treatment, they are
             eligible if they have an undetectable HCV viral load

          -  Patients with treated brain metastases are eligible if follow-up brain imaging after
             central nervous system (CNS)-directed therapy shows no evidence of progression.
             Furthermore, these patients must be asymptomatic from previously treated brain
             metastases (e.g. not on steroids for neurologic symptoms within 30 days of study
             enrollment)

          -  Patients with a prior or concurrent malignancy whose natural history or treatment does
             not have the potential to interfere with the safety or efficacy assessment of the
             investigational regimen are eligible for this trial

          -  Patients with known history or current symptoms of cardiac disease, or history of
             treatment with cardiotoxic agents, should have a clinical risk assessment of cardiac
             function using the New York Heart Association Functional Classification. To be
             eligible for this trial, patients should be class 2B or better

          -  The effects of BAY 1895344 on the developing human fetus are unknown. For this reason
             and because DNA-damage response inhibitors as well as other therapeutic agents used in
             this trial are known to be teratogenic, women of child-bearing potential and men must
             agree to use adequate contraception (hormonal or barrier method of birth control;
             abstinence) prior to study entry and for the duration of study participation and for 6
             months after completion of BAY 1895344 administration. Should a woman become pregnant
             or suspect she is pregnant while she or her partner is participating in this study,
             she should inform her treating physician immediately. Men treated or enrolled on this
             protocol must also agree to use adequate contraception prior to the study, for the
             duration of study participation, and 6 months after completion of BAY 1895344
             administration

          -  Patient must have the ability to understand and the willingness to sign a written
             informed consent document. Participants with impaired decision-making capacity (IDMC)
             who have a legally-authorized representative (LAR) and/or family member available will
             also be eligible

        Exclusion Criteria:

          -  Patients who have had chemotherapy or radiotherapy within 4 weeks (6 weeks for
             nitrosoureas or mitomycin C) prior to entering the study

          -  Patients who have not recovered from adverse events due to prior anti-cancer therapy
             (i.e., have residual toxicities > grade 1) with the exception of alopecia

          -  Patients who are receiving any other investigational agents

          -  The investigator(s) must state a medical or scientific reason if patients who have
             brain metastases will be excluded from the study

          -  History of allergic reactions attributed to compounds of similar chemical or biologic
             composition to BAY 1895334 or other agents used in study

          -  Patients receiving any medications or substances that are substrates of CYP3A4 with a
             narrow therapeutic window, or strong inhibitors/inducers of CYP3A4 are ineligible, if
             they cannot be transferred to alternative medication. Because the lists of these
             agents are constantly changing, it is important to regularly consult a
             frequently-updated medical reference. As part of the enrollment/informed consent
             procedures, the patient will be counseled on the risk of interactions with other
             agents, and what to do if new medications need to be prescribed or if the patient is
             considering a new over-the-counter medicine or herbal product

          -  Patients with uncontrolled intercurrent illness

          -  Patients with psychiatric illness/social situations that would limit compliance with
             study requirements

          -  Pregnant women are excluded from this study because BAY 1895344 is agent with the
             potential for teratogenic or abortifacient effects. Because there is an unknown but
             potential risk for adverse events in nursing infants secondary to treatment of the
             mother with BAY 18953354, breastfeeding should be discontinued if the mother is
             treated with BAY 18953354. These potential risks may also apply to other agents used
             in this study

          -  Patients with an uncontrolled infection requiring IV antibiotics will not be eligible
             to participate in the study

          -  Patients who have previously been treated with any of the study compounds will not be
             eligible to participate in the study