Immunophenotype. These tumors express the B cell antigen CD20. Many also express surface IgM and/or IgG. Other antigens (e.g., CD10, BCL2) are variably expressed.
Fig. 12.17 DiffuselargeBcelllymphoma—lymphnode.Thetumorcellshavelargenucleiwithopenchromatinandprominentnucleoli.(Courtesy of Dr.Robert W.McKenna,Department of Pathology,University of Texas Southwestern Medical School, Dallas,Texas.)
Special Subtypes. Several distinctive clinicopathologic subtypes are included in the category of diffuse large B cell lymphoma.
EBV-associated diffuse large B cell lymphomas arise in the setting of AIDS, iatrogenic immunosuppression (e.g., in transplant recipients), and the elderly. In the posttransplantation setting, these tumors often begin as EBV-driven polyclonal B cell proliferations that may regress if immune function is restored.
Kaposi sarcoma herpesvirus (KSHV), also called human herpesvirus type 8 (HHV-8), is associated with rare primary effusion lymphomas, which may arise within the pleural cavity, pericardium, or peritoneum. These tumors are latently infected with KSHV, which encodes proteins homologous to several known oncoproteins, including cyclin D1. As with EBV-related lymphomas, most affected patients are immunosuppressed.
Mediastinal large B cell lymphoma occurs most often in young women and shows a predilection for spread to abdominal viscera and the central nervous system.
Clinical Features. Although the median age at presentation is about 60 years, diffuse large B cell lymphoma can occur at any age; it constitutes about 15% of childhood lymphomas. Patients typically present with a rapidly enlarging, often symptomatic mass at one or several sites. Extranodal presentations are common. The gastrointestinal tract is the most common extranodal site, but tumors can appear in virtually any organ or tissue. Unlike the more indolent lymphomas (e.g., follicular lymphoma), involvement of the liver, spleen, and bone marrow is not common at diagnosis.
Without treatment, diffuse large cell B cell lymphomas are aggressive and rapidly fatal. With intensive combination chemotherapy and anti-CD20 immunotherapy, complete remissions are achieved in 60% to 80% of the patients; of these, approximately 50% remain free of disease and appear to be cured. For those not so fortunate, other aggressive treatments (e.g., high-dose chemotherapy and hematopoietic stem cell transplantation) offer some hope.
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Burkitt lymphoma is endemic in parts of Africa and occurs sporadically in other geographic areas, including the United States. Histologically, the African and nonendemic diseases are identical, although there are clinical and virologic differences.
Burkitt lymphoma is highly associated with translocations involving the MYC gene on chromosome 8 that result in overexpression of the MYC transcription factor.
As mentioned in Chapter 6, MYC is a master regulator of Warburg metabolism (aerobic glycolysis), a cancer hallmark that is associated with rapid cell growth. In keeping with this association, Burkitt lymphoma is said to be the fastest growing human tumor. Most translocations fuse MYC with the IgH gene on chromosome 14, but variant translocations involving the κ or λ light chain loci also are observed. The net result of each is the same—the dysregulation and overexpression of MYC. In most endemic cases and about 20% of sporadic cases, the tumor cells are latently infected with EBV, a relationship also discussed in Chapter 6.