Bispecific T-Cell Engager Tarlatamab and TROP2 Targeted Antibody Drug Conjugate Sacituzumab Govitecan in Previously Treated Extensive-Stage Small Cell Lung Cancer and Extrapulmonary Neuroendocrine Cancer

* INCLUSION CRITERIA:
* Must have histologically or cytologically confirmed SCLC or EP-NEC meeting the criteria below:

  * SCLC that has progressed or recurred after a combination of platinum-based regimen and immunotherapy. Participants may be eligible after treatment with chemo or immunotherapy alone if they were intolerant to one of the components. Participants with previously locally advanced SCLC who have completed definitive chemoradiation therapy, with or without surgical resection, and subsequently experienced disease progression or recurrence, are also eligible. OR
  * EP-NEC that has progressed or recurred after at least one prior chemotherapy.
* Must have measurable disease, per RECIST 1.1
* Age \>=18 years.
* Eastern Cooperative Oncology Group (ECOG) performance status \<=2.
* Must have adequate organ and marrow function as defined below:

System/Laboratory Value

Hematological

* Hemoglobin/\>=9 g/dL(a)
* Absolute neutrophil count/\>= 1,500/mcL
* Platelets/\>= 100,000/mcL

System/Laboratory Value

Hepatic

* Total bilirubin/within normal institutional limits
* AST (SGOT) and ALT (SGPT) \<= 2.5 X institutional ULN (\<=5 X ULN for participants with liver metastases)

Renal

-Creatinine/ within normal institutional limits

OR

-Calculated (b) creatinine clearance (GFR can also be used in place of creatinine or CrCl)/\>=60 mL/min for participant with creatinine levels above institutional normal

OR

Coagulation

* Prothrombin time (PT) \<=1.5 x ULN unless participant is receiving anticoagulant therapy if PT or PTT is within therapeutic range of intended use of anticoagulants
* Partial thromboplastin time (PTT) \<=1.5 x ULN unless participant is receiving anticoagulant therapy if PT or PTT is within therapeutic range of intended use of anticoagulants

ALT (SGPT)=alanine aminotransferase (serum glutamic pyruvic transaminase);

AST (SGOT)=aspartate aminotransferase (serum glutamic oxaloacetic transaminase);

GFR=glomerular filtration rate; ULN=upper limit of normal.

1. Criteria must be met without erythropoietin dependency and without packed red blood cell (pRBC) transfusion within last 2 weeks.
2. Creatinine clearance (CrCl) should be calculated per institutional standard.

   * Individuals with neurologically stable brain metastases defined as asymptomatic metastasis, or treated metastasis having no evidence of progression or hemorrhage for at least 1 week after treatment (including brain radiotherapy) may be included. Individuals must be off any systemic corticosteroids for the treatment of brain metastases for at least 7 days prior to study drug initiation.
   * Individuals with human immunodeficiency virus (HIV) must be on effective antiretroviral therapy with undetectable viral load at screening.
   * Individuals with evidence of chronic hepatitis B virus (HBV) infection must have undetectable HBV viral load at screening.
   * Individuals with a history of hepatitis C virus (HCV) infection must have been treated and cured. Individuals with active HCV infection who are currently on treatment are eligible if they have an undetectable HCV viral load at screening.
   * Must agree to use an effective method of contraception (barrier, hormonal, intrauterine device \[IUD\], surgical sterilization, abstinence) during study treatment and for 3 months thereafter for males or 6 months for women of childbearing potential (WOCBP).
   * Willingness to discontinue nursing during study treatment and for 2 months after the last dose of study treatment.
   * Ability to understand and the willingness to sign a written informed consent document.

EXCLUSION CRITERIA:

* Receiving any other investigational agents or concurrent systemic anti-cancer therapies. Any previous non-investigational treatment must be completed at least 2 weeks prior to study drug initiation.
* Prior exposure to tarlatamab or other DLL3-targeting agents/T-cell engagers (TCE).
* Requiring radiation therapy during study treatment. Radiation therapy may be allowed if needed for palliative/symptom control (e.g., bone metastasis) but must be completed at least 7 days before study drug initiation.
* Severe and unresolved active autoimmune inflammatory conditions.
* Pregnant women, breastfeeding women, and women planning to become pregnant or donate eggs should not take part in this study.
* Requiring immunosuppressive agents with the exception of those required by protocol, treatment for adverse events, Central Nervous System (CNS) metastases corticosteroid replacement therapy.
* Require live and live-attenuated vaccines during study treatment with tarlatamab or within 4 weeks of first dose of tarlatamab. Examples of live vaccines include, but are not limited to, the following: measles, mumps, rubella, chicken pox, yellow fever, rabies, Bacillus Calmette-Guerin (BCG), and typhoid (oral) vaccine. Seasonal influenza vaccines for injection are generally killed virus vaccines and are allowed. However, intranasal influenza vaccines (e.g., Flu-Mist) are live attenuated vaccines and are not allowed.
* History of allergic reactions attributed to compounds of similar chemical or biologic composition to study drugs or other agents used in study.
* Requiring treatment with inhibitors or inducers of UGT1A1 during the planned period of study treatment.
* QTc \>= 470 msec or any conditions or factors that may increase the risk of QTc prolongation.
* Uncontrolled intercurrent illness, evaluated by medical history and physical exam which would potentially increase risk to the participant.