Assessment for acceleration and transformation of chronic lymphocytic leukemia/small lymphocytic lymphoma using histologic and immunohistochemical features: a case series.

Morphologic features of aggressive/ "accelerated" chronic lymphocytic leukemia/small lymphocytic lymphoma (aCLL/SLL) have been described. Richter transformation (RT) also occurs in a subset of CLL/SLL cases. This case series examined inter-observer variability when assessing for aCLL/SLL and RT, with attention to how immunohistochemical (IHC) markers may assist in this evaluation. Twelve cases of CLL/SLL with available FFPE tissue were identified. H&E staining and IHC (CD3, CD20, CD5, CD23, LEF1, LAG3, C-MYC, PD-1, MUM1, Cyclin D1, BCL-6, p53, and Ki-67) were performed. Three hematopathologists reviewed each case. The pathologists provided a final interpretation of (1) CLL/SLL, (2) CLL/SLL with expanded and/or confluent proliferation centers or increased Ki-67 (aCLL/SLL), or (3) large cell transformation/DLBCL. The pathologists lacked consensus in the diagnosis in 6/12 cases (50%). The reviewers disagreed on the presence of expanded/confluent proliferation centers in 8/12 cases (67%). With the exception of Ki-67, no IHC marker showed a difference in the staining profile in aCLL/SLL or RT compared to low-grade cases. This series showed inter-observer variability in the evaluation for aCLL/SLL and RT. A study that serially examines genetic alterations in FFPE tissue and correlates the features with histology and IHC, at diagnosis and throughout the disease course, may help refine indicators of aggressive disease.