ALK-positive anaplastic large cell lymphoma mimicking nodular sclerosis Hodgkin's lymphoma: report of 10 cases.

Anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL) are recognized as biologically distinct entities. However, occasionally, these two entities may share some morphologic features responsible for diagnostic difficulties. In the last 10 years, we have collected 380 cases of ALK-positive ALCL of which 10 cases were originally diagnosed as nodular sclerosis classic HL (NSHL) on conventional histopathological examination. After immunostaining, these cases proved to be ALK-positive ALCL mimicking HL (so-called Hodgkin-like ALCL). These cases account for 2.6% of our cases of ALK-positive ALCL (10 of 380 cases). Median age was 11 years (3-92 years) with a female predominance (male/female ratio, 3:7). Characteristically, these lesions showed thick nodular fibrosing bands highly suggestive of NSHL. Neoplastic cells were scarce in 6 cases, whereas in the 4 remaining cases, sheets of tumor cells were also present. A perivascular and a sinusoidal growth pattern was observed in various degrees in all cases. Few binucleated Reed-Sternberg-like cells were present in every case in a background of small lymphocytes. Inflammatory cells (ie, granulocytes, eosinophils, and histiocytes) were rare. Neoplastic cells were positive for CD30 (10 of 10 cases), ALK protein (10 of 10 cases), epithelial membrane antigen (EMA) (9 of 9 cases), CD43 (6 of 9 cases), and perforin (8 of 8 cases), but negative for CD15 (10 of 10 cases), CD20 (10 of 10 cases), Pax5/BSAP (6 of 6 cases), and EBV (8 of 8 cases). In addition, in 7 cases, neoplastic cells were of T-phenotype, whereas the 3 remaining cases were considered to be of null/undetermined phenotype. Although rare, Hodgkin-like ALCL may mimic NSHL, and it is advisable to include EMA in the first line panel and to ask for ALK staining in EMA-positive, CD15-negative lesions with morphologic features suggestive of NSHL.