When pseudo-Richter transformation hits the spleen: a case report and literature review.

Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is the most prevalent leukemia in adults which typically follows an indolent clinical course. However, it has the potential to transform into more aggressive categories, including accelerated CLL or diffuse large B-cell lymphoma (DLBCL), a phenomenon known as Richter transformation. Bruton tyrosine kinase inhibidors (BTKI), such as ibrutinib and zanubrutinib, represent a cornerstone of CLL/SLL treatment by inhibiting B-cell receptor signaling. Temporary discontinuation of these agents are common due to surgical procedures or infections which has been associated with rapid disease progression, producing a pseudo-Richter transformation (P-RT) in tissues. We present a case with CLL/SLL who experienced clinical deterioration following ibrutinib withdrawal, resulting in an explosive disease flare and splenic rupture. The patient improved after BTKI reintroduction, and a P-RT was diagnosed. Nine similar patients were found through PubMed search, and we describe their clinicopathological characteristics.