Histologic transformation in marginal zone lymphomas

Background: Histologic transformation ( HT) is a poorly understood event in patients with marginal zone lymphoma ( MZL). The aim of this study was to analyze incidence and risk factors for HT in a large series of MZL patients. Patients and methods: The studied cohort included 340 MZL patients diagnosed and treated between 1995 and 2012: 157 extranodal MZLs [ mucosa- associated lymphoid tissue ( MALT) lymphoma, 46%], 85 splenic MZLs ( SMZLs, 25%) and 37 nodal MZLs ( NMZLs, 11%). Sixty- one patients ( 18%) had bone marrow infiltration at presentation, with or without detectable involvement of peripheral blood, but without other involved sites; they were considered clonal B- cell lymphocytosis of marginal zone origin ( CBL- MZ). Results: With a median follow- up of 4.8 years, the median overall survival and progression- free survival of the whole population were 14.5 and 5 years, respectively. HT was observed in 13 cases [ 3.8%, 95% confidence interval ( 95% CI) 2%- 6.5%]. Elevated lactate dehydrogenase ( LDH) at diagnosis was associated with the risk of HT ( P = 0.019). HT occurred in 5% of SMZLs, 4% of MALT lymphomas, 3% of NMZLs and 3% of CBL- MZ ( P = 0.974). The risk of HT was 5% ( 95% CI 3- 9%) at 5 and 10 years after diagnosis and 10% ( 95% CI 5%- 20%) at 12 years. At the time of HT, most patients had high LDH and B symptoms. At a median follow- up of 12 months after HT, 4 of 13 patients died, all for lymphomarelated causes, with a 2- year post- transformation survival rate of 57% ( 95% CI 13%- 86%). Conclusions: In this large retrospective series, the risk of HT across all MZL types appeared lower than the one reported for follicular lymphoma.