#00063883

An 83-year-old man presented with lymphadenopathy. Left pelvic lymph node biopsy showed fragments of lymphoid tissue involved by two different neoplasms. The major component is composed of small lymphocytes with round nuclear contours, clumped chromatin, inconspicuous nucleolus and small amount of cytoplasm. The minor component is composed of large atypical cells with round to oval nuclear contours with or without nuclear groove, vesicular chromatin, distinct small nucleoli, and abundant pink cytoplasm, with increased mitotic figures. These two components were not well-demarcated and showed a transition with the large, atypical cells gradually decreasing where small lymphocytes gradually predominate. Lymph node biopsy was diagnosed as Small lymphocytic lymphoma (SLL, original magnification ×20) and histiocytic sarcoma (HS, original magnification ×40).

Immunohistochemical stains showed that the SLL component is positive for CD5, LEF1, and PAX5 and negative for CD56. The histiocytic sarcoma component is positive for CD4, CD11c and CD56, and negative for PAX5 (immunohistochemical stains, original magnification x20). IGH gene rearrangement testing showed monoclonality with identical peaks from the two separate components, supporting a clonal relationship.

This rare case has shown the evidence of cross-lineage trans differentiation and transformation of low-grade hematopoietic tumor (SLL) into aggressive hematopoietic tumor of another lineage (HS).