P16, c-Myc, SOX11, P53, ki67 and CD71Protein Expression in Aggressive Morphological Variants of Mantle Cell Lymphomas Compared to Classical Morphological Mantle Cell Lymphomas in Multiple Clinical Trials

On behalf of the Lymphoma Study Association (LYSA)

Introduction: Aggressive Mantle Cell Lymphoma variant (A-MCL), including blastic and pleomorphic morphological variants, is a rare subtype of MCL whose frequency varies around 10-15% of all newly-diagnosed MCL patients. According to 2017 World Health Organization (WHO) classification, the diagnosis of A-MCL is based on morphology. A high proliferation rate on Ki-67 staining is not sufficient to be classified as a blastoid or pleomorphic subtype. This might induce diagnostic confusion. The aim of the present retrospective study is to investigate whether or not the CD71, c-Myc, SOX11, P53, ki67 and P16 expressions assessed by immunohistochemistry (IHC) can distinguish A-MCL from classical MCL (C-MCL). We also investigate the prognostic value of these markers in A-MCL patients.

Methods: We re-investigated all MCL patients presented with A-MCL (n=110) at diagnosis and who have been enrolled in six prospective clinical trials. At time of inclusion, a centralized pathological review was performed to confirm the diagnosis of MCL. Cases were initially classified according to the 2008 WHO classification (LYMA, MCL-SA, MCL-SJ, RIBVD and RIPAD trials) or according to the 2017 WHO classification (MCLR2-ELDERLY trials). For the present study, we performed a supplemental pathology review by a panel of 5 hematopathologists experts from the LYSA group according to 2017 WHO classification. We identified 75 cases (out of 110) of A-MCL (8 blastic and 67 pleomorphic variants) which represent 15% of all MCL enrolled in these six trials. We have compared A-MCL characteristics to C-MCL who had specimens available for TMA (n=412 C-MCL out of 487 patients enrolled). IHC was performed on TMA, using the six selected antibodies and were scored by quantifying the percentage of cells stained on each spot. Patients available for survival analysis (53 A-MCL and 312 C-MCL) were drawn from all studies (except from the MCLR2-Elderly study that is ongoing). Different cut-offs were considered for progression free survival (PFS) and overall survival (OS) for each variable. The proliferation index was evaluated with Ki67 classical determination eyeballing and Ki67 reading by grid counting. Cut-offs for each of these markers were determined using X-tile software, which determines the optimal value for classifying patients into groups based on overall and progression-free survival.

Results: At baseline, the aggressive forms were similar to classical forms in terms of demographic characteristics (age at diagnosis, localization and sex). p53 protein expression was significantly higher in A-MCL patients than in C-MCL (p<0.001) like p16 (p=0.002), c-MYC (p<0.001), CD71 (p<0.001) and Ki67 index (both classical and by grid) (p< 0.001). There was no statistically significant difference in SOX11 expression. In univariate analyses, elevated levels of P16 (>10%), c-MYC (>30%) Ki67 (>40%) were associated with poorer OS and PFS in the cohort of A-MCL and C-MCL patients. There was no significant difference in survival both for OS and PFS regarding P53 (>30%). In multivariate analysis stratified by trial, Ki67 by grid>40% (HR=2.303[1.479-3.585] ; p =0.0002) and c-MYC >30% (HR=1.865 [1.060-3.279] p =0.0305) were predictive for OS whereas only Ki67 by grid >40% (HR=2.055 [1.434, 2.944], p<0.0001) was a significant prognostic factor for PFS.

Conclusion: CD71, c-Myc, P53 and P16 expression levels assessed by IHC are higher in A-MCL as compared to C-MCL. These markers could therefore be recommended in routine practice to distinguish between A-MCL and C-MCL. We also found that patients with Ki67 count by grid >40% had significantly shorter PFS and OS and patients with high Myc expression >30% had a significantly poorer OS. Thus, MYC expression and Ki67 by IHC is a suitable test for routine diagnostic practice to assess A-MCL prognosis.