Primary mediastinal large B-cell lymphoma (PMBCL) is a form of DLBCL arising in the mediastinum from the thymic B cell. It is an uncommon entity and has clinical and pathologic features distinct from systemic DLBCL [64]. PMBCL accounts for 2% of all NHLs and about 7% of all DLBCL [20]. It typically affects women in the third to fourth decade of life.
Presentation and Prognostic Features
PMBCL usually presents as a locally invasive anterior mediastinal mass, often with a superior vena cava syndrome which may or may not be clinically obvious [64]. Other presentations include pericardial tamponade, thrombosis of neck veins, and acute airway obstruction. About 80% of patients present with bulky (> 10 cm) stage I or II disease [65], with distant spread uncommon on presentation. Morphologically and on GEP, PMBL has a profile more similar to classical Hodgkin lymphoma (cHL) than non-mediastinal DLBCL [66]. PMBL is distinguished from cHL by immunophenotyping: unlike cHL, PMBCL has pan B cell markers, rarely expresses CD15, and has weak CD30.
Poor prognostic features in PMBCL are Eastern Cooperative Oncology Group (ECOG) performance status greater than 2, pericardial effusion, bulky disease, and elevated serum LDH. The diagnosis of PMBCL can be difficult because the tumor is often encased with extensive fibrosis and necrosis. As a result, a needle biopsy may not yield sufficient tissue, thus making a surgical biopsy often the only viable way to obtain sufficient tissue.
Treatment
Early series suggested that PMBCL is unusually aggressive, with a poor prognosis [67]. This led to studies using more aggressive chemotherapy regimens (often in combination with mediastinal radiation) as well as upfront auto-HCT [68–70]. The addition of rituximab to treatment regimens significantly improved outcomes in PMBCL. For example, a subgroup analysis of the PMBCL patients in the MinT trial revealed a 3-year event-free survival (EFS) of 78% [71] when rituximab was combined with CHOP. Because of previous reports demonstrating radiosensitivity of PMBL, radiation was traditionally sequenced into treatment regimens for PMBL. However, this is associated with higher long-term toxicities, often a concern in PMBCL patients given that the disease frequently affects younger females, and given that breast tissue will be in the radiation field. For patients with a strong personal or family history of breast cancer or cardiovascular disease, these concerns are even more significant. More recently, the DA-EPOCH-R regimen has been shown to produce very high rates (80%–90%) of long-term DFS, without the need for mediastinal radiation in most cases [72,73]. For patients receiving R-CHOP, consolidation with mediastinal radiation is still commonly given. This approach also leads to high rates of long-term remission and, although utilizing mediastinal radiation, allows for less intensive chemotherapy. Determining which approach is most appropriate for an individual patient requires an assessment of the risks of each treatment option for that patient. A randomized trial by the International Extranodal Lymphoma Study Group (IELSG37) is evaluating whether RT may be safely omitted in PMBCL patients who achieve a complete metabolic response after R-CHOP.
Most relapses of PMBCL occur within the first 1 to 2 years and often present with extranodal disease in various organs. For those with relapsed or refractory disease, high-dose chemotherapy followed by auto-HCT provides 5-year survival rates of 50% to 80% [74–76] In a phase 1b trial evaluating the role of pembrolizumab in relapsed/refractory patients (KEYNOTE-13), 7 of 17 PMBCL patients achieved responses, with an additional 6 demonstrating stable disease [77]. This provides an additional option for patients who might be too weak to undergo auto-HCT or for those who relapse following auto-HCT.
Mantle Cell Lymphoma
The name mantle cell lymphoma (MCL) is based on the presumed normal cell counterpart to MCL, which is believed to be found in the mantle zone surrounding germinal center follicles. It represents approximately 6% of all NHL cases in the United States and Europe [78] MCL occurs at a median age of 63 to 68 years and has a male predominance.
Presentation and Prognostic Features
Patients can present with a broad spectrum of clinical features, and most patients (70%) present with advanced disease [79]. Up to one third of patients have B symptoms, with most demonstrating lymphadenopathy and bone marrow involvement. Approximately 25% present with extranodal disease as the primary presentation (eg, GI tract, pleura, breast, or orbits). MCL can involve any part of the GI tract and often presents as polypoid lesions.
Histologically, the pattern of MCL may be diffuse, nodular, mantle zone, or a combination of the these; morphologically, MCL can range from small, more irregular lymphocytes to lymphoblast-like cells. Blastoid and pleomorphic variants of MCL have a higher proliferation index and a more aggressive clinical course than other variants. MCL is characterized by the expression of pan B cell antigens (CD19+, CD20+) with coexpression of the T-cell antigen CD5, lack of CD23 expression, and nuclear expression of cyclin D1. Nuclear staining for cyclin D1 is present in more than 98% of cases [80]. In rare cases, CD5 or cyclin D1 may be negative [80]. Most MCL cases have a unique translocation that fuses the immunoglobulin heavy chain gene promoter (14q32) to the promoter of the BCL-1 gene (11q13), which encodes the cyclin D1 protein. This translocation is not unique to MCL and can be present in multiple myeloma as well. Interestingly, cyclin D1 is overproduced in cases lacking t(11:14), likely from other point mutations resulting in its overexpression [81]. Cyclin D1–negative tumors overexpress cyclin D2 or D3, with no apparent difference in clinical behavior or outcome [82]. In cyclin D1–negative cases, SOX11 expression may help with diagnosis [83]. A proliferation rate greater than 30% (as measured by Ki-67 staining), low SOX11 expression, and presence of p53 mutations have all been associated with adverse outcome.
In a minority of cases, MCL follows an indolent clinical course. For the remainder, however, MCL is an aggressive disease that generally requires treatment soon after diagnosis. When initially described in the 1980s and 1990s, treatment of MCL was characterized by low complete response rates, short durations of remission, repeated recurrences, and a median survival in the 2- to 5-year range [84]. In recent years, intensive regimens incorporating rituximab and high-dose cytarabine with or without auto-HCT have been developed and are associated with high complete response rates and median duration of first remission in the 6- to 9-year range [85–87]. Several prognostic indices have been applied to patients with MCL, including the IPI, the Follicular Lymphoma International Prognostic Index , and the Mantle Cell Lymphoma International Prognostic Index (MIPI). The MIPI was originally described based on a cohort from the period 1996 to 2004 [88], and subsequently confirmed in a separate cohort of 958 patients with MCL treated on prospective trials between 2004 and 2010 [89]. The MIPI score can identify 3 risk groups with significant survival differences (83%, 63%, and 34% survival at 5 years). A refined version of the MIPI score, the combined MIPI or MIPI-c, incorporates proliferation rate and is better able to stratify patients [90]. The blastoid variant of MCL follows a more aggressive clinical course and is associated with a high proliferation rate, shorter remissions, and a higher rate of CNS involvement [91].
In most patients, MCL is an aggressive disease with a short OS without treatment. A subset of patients may have a more indolent course [92], but unfortunately reliable factors that identify this group at the time of diagnosis are not available. Pretreatment evaluation is as with other lymphomas, with lumbar puncture and MRI of the brain also recommended for patients with the blastoid variant. For those presenting with GI symptoms, endoscopy is recommended as part of the initial evaluation as well.
