Anaplastic large cell lymphoma (ALCL) is a distinct entity with the phenotype of activated mature cytotoxic T cells, characterized by the proliferation of usually large, pleomorphic CD30-positive cells with a kidney-shaped nucleus. Two definitive entities are recognized in the revised WHO classification: ALCL, ALK-positive defined by the presence of a chromosomal rearrangement that involves the ALK gene resulting in the expression of the ALK protein  and ALCL, ALK-negative that has similar features to ALK-positive cases but lacks translocations involving ALK and expression of the protein . Another form of ALCL, breast implant-associated ALCL, has been included in the revised WHO classification as a provisional entity . ALCL should be distinguished from primary cutaneous ALCL (see Chapter 18) and from other CD30-positive T- and B-cell derived lymphomas.
ALK-positive ALCL affects predominantly young adults and children whilst ALK-negative ALCL is a disease of adults. There is a slight male predominance. Most patients present with B symptoms and advanced stage disease; involvement of extranodal sites such as skin and bone is frequent. Breast implant-associated ALCL is seen in female patients with breast implants and usually presents with disease localized to the breast.
Haematological and pathological features
The tissue or lymph node involved is often diffusely infiltrated by the neoplastic T cells (Figures 23.1, 23.2, 23.3). Rarely the cells are only present in the sinuses or in the T-cell areas. Circulating neoplastic cells are sometimes present (Figures 23.4 and 23.5). There is a wide cytological spectrum in both ALK-positive and ALK-negative ALCL. Regardless of the histological pattern, all cases have the so-called “hallmark” cells. These cells are usually large with a kidney-shaped nucleus and an eosinophilic area next to the nucleus. Sometimes they have an invaginated nucleus that gives the appearance of nuclear inclusions (doughnut cells). In the most frequent pattern, seen in about two thirds of cases, most of the cells are large with abundant cytoplasm and multiple nuclei. Some cells may resemble Reed–Sternberg cells. Other less frequent patterns are the lymphohistiocytic pattern that shows a mixture of neoplastic cells and histiocytes, the small-cell pattern where the predominant neoplastic population is small or medium sized with larger cells located around the vessels and the Hodgkin-like pattern that resembles nodular sclerosis classical Hodgkin lymphoma. Some cases have one or more patterns in the same tissue and others may relapse with a pattern different from that shown at presentation.
Bone marrow infiltrated by ALK-positive anaplastic large cell lymphoma (ALCL) showing large cells, one with a multilobated nucleus and prominent nucleoli. Romanowsky stain, ×100 objective.
Lymph node section in ALK-positive ALCL showing anaplastic cellular morphology with large cells having irregular and pleomorphic nuclei including ...