Nemtabrutinib and Pembrolizumab for the Treatment of Richter Transformation, Diffuse Large B-cell Lymphoma Subtype

Inclusion Criteria: * Patients with biopsy-proven Richter transformation, diffuse large B-cell lymphoma subtype (RT-DLBCL) from an antecedent or concurrently diagnosed chronic lymphocytic leukemia (CLL) and/or small lymphocytic lymphoma (SLL). * Be ineligible for frontline anthracycline-based chemoimmunotherapy (determined by treating investigator) OR have clinical evidence of disease progression after any prior treatment for RT-DLBCL. * Participants who have adverse events (AEs) due to previous anti-cancer therapies must have recovered to ≤ grade 1 or baseline. Participants with endocrine-related AEs who are adequately treated with hormone replacement or participants who have ≤ grade 2 neuropathy are eligible. * Note: Participants who have lingering cytopenias from prior anti-cancer therapy or progressive disease may be eligible at the discretion of the study principal investigator (PI), provided they meet all other study criteria. * Have measurable disease as determined by imaging (by positron-emission tomography \[PET\] and/or computed tomography \[CT\] scans), immunohistochemistry, and/or flow cytometry, as per the Cheson criteria. * Have the ability to swallow and retain oral medication. * Age 18 years and older on the day of signing informed consent. * Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2. * Be free from other malignancy within 2 years prior to enrollment (with the exception of CLL/SLL, low-risk and early stage \[T1-T2a- Gleaso…