This phase II trial studies the effects of niraparib in combination with dostarlimab prior to surgery in treating BRCA-mutated or PALB2-mutated stage I-III breast cancer. Niraparib is a PARP inhibitor, which means that it blocks an enzyme (proteins that help chemical reactions in the body occur) in cells called PARP. PARP helps repair deoxyribonucleic acid (DNA) when it becomes damaged. Blocking PARP may help keep cancer cells from repairing their damaged DNA, causing them to die. PARP inhibitors are a type of targeted therapy. Dostarlimab stimulates the immune system by blocking the PD-1 pathway. The PD-1 pathway controls the bodys natural immune response, but for some types of cancer, the immune system does not work as it should and is prevented from attacking tumors. Dostarlimab works by blocking the PD-1 pathway, which may help your immune system identify and catch tumor cells. Giving niraparib in combination with dostarlimab may work better against the tumor and maximize tumor shrinkage before surgery.

Severe Aplastic Anemia (SAA) is a rare condition in which the body stops producing enough new
blood cells. SAA can be cured with immune suppressive therapy or a bone marrow transplant.
Regular treatment for patients with aplastic anemia who have a matched sibling (brother or
sister), or family donor is a bone marrow transplant. Patients without a matched family donor
normally are treated with immune suppressive therapy (IST). Match unrelated donor (URD) bone
marrow transplant (BMT) is used as a secondary treatment in patients who did not get better
with IST, had their disease come back, or a new worse disease replaced it (like leukemia).

This trial will compare time from randomization to failure of treatment or death from any
cause of IST versus URD BMT when used as initial therapy to treat SAA.

The trial will also assess whether health-related quality of life and early markers of
fertility differ between those randomized to URD BMT or IST, as well as assess the presence
of marrow failure-related genes and presence of gene mutations associated with MDS or
leukemia and the change in gene signatures after treatment in both study arms.

This study treatment does not include any investigational drugs. The medicines and procedures
in this study are standard for treatment of SAA.