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Clinical presentation determines selection of patients for initial observation in mantle cell lymphoma

Mantle cell lymphoma (MCL) is clinically and biologically heterogeneous, and while a subset of cases is observed initially, clinical and biological selection criteria to identify candidates for this strategy are not well defined. We hypothesized that the decision to monitor a patient should be made on the basis of clinical criteria, as is standard for chronic lymphocytic leukemia and other indolent B-cell non-Hodgkin lymphomas. Patients with leukemic non-nodal MCL are optimal candidates for initial observation, but those who meet other criteria, such as microscopic gastrointestinal (GI) tract involvement or low-volume nodal disease, are also potential candidates. Although biological criteria such as proliferation rate and TP53 mutation status have prognostic significance in MCL, we hypothesized that these unfavorable biological features do not disqualify asymptomatic patients from initial observation. In this retrospective analysis, we describe the clinical and biological characteristics of MCL patients who were initially observed versus immediately treated, and the associated outcomes. Eligible adult patients had histologically confirmed MCL diagnosed between 2000 and 2014 and were managed at Memorial Sloan Kettering Cancer Center (MSK). Initial observation was defined as treatment deferral for at least three months after diagnosis with documentation of an ‘intent to observe’ by the treating oncologist. There were no predefined clinical or biological criteria for observation. The study was approved by the MSK Institutional Review Board. Fisher exact or Wilcoxon rank sum tests were used to compare the baseline characteristics of the immediate and deferred treatment groups. Cox regression modeling was used to analyze the time from tumor diagnosis to initiation of any treatment (TTI) in the observation group and overall survival (OS; defined as time from tumor diagnosis to death from any cause). Statistical significance was defined as P<0.05. All analyses were completed with R version 3.5.0. A data freeze was instituted on September 2, 2015. We identified 404 untreated patients with histologically confirmed MCL who were managed at MSK: 90 were initially observed (OBS) and 314 were immediately treated (TX). Reasons for observation documented by the treating oncologist included: lack of symptoms, low tumor burden, perceived favorable biological features (low Ki-67 or SOX-11 negativity), leukemic phase disease without lymphadenopathy, or disease limited to GI tract. None of the OBS patients had significant constitutional symptoms, progressive marrow failure manifest by anemia and/or thrombocytopenia, symptomatic organomegaly, progressive or symptomatic nodal enlargement, or evidence of clinically significant organ compression or involvement. The baseline characteristics of the OBS versus TX patients are shown in Table 1. Among the 90 OBS patients, 64 were started on therapy after a period of observation while 26 were expectantly monitored. The median time of observation was 23 months (Figure 1A). Among the OBS patients who were subsequently treated, 23 (36%) were observed for 12 months or longer, 21 (33%) for 1-2 years, and 20 (31%)