Bio-O1-02 - Deciphering discrepancies in cutaneous lymphomas genetics

Abstract

In several instances, our group has reported opposite findings to others when analyzing the genetic features of primary cutaneous T-cell or B-cell lymphomas (CTCL or CBCL). This was especially the case for the absence of NAV3 rearrangements in CTCL, the low rate of BCL2 or MYC rearrangement in primary cutaneous follicle center lymphomas (CFCL) or primary cutaneous large B-cell lymphomas, leg-type (CLBCL, LT), respectively. Here, we review bias accounting for such discrepancies. Primary cutaneous lymphoma usually present with characteristic clinical and pathological features which serve as universal criteria for initial diagnosis and treatment. When required, extensive staging including CT scan, blood analysis and for some groups bone marrow staging, is mandatory to eliminate a secondary CTCL or CBCL. Early spreading may change the initial diagnosis and a long-term follow-up is also necessary to determine the risk for extracutaneous involvement. Non-uniform inclusion criteria and follow-up time may contribute to discrepancies, especially for studies claiming for a high rate of BCL2 rearrangement in CBCL. Most CBCL or CTCL usually display an indolent course except for aggressive subtypes arising de novo such as Sézary syndrome (SS), tumor or transformed mycosis fungoides (T-MF) or CLBCL-LT. Borderline cases between indolent and aggressive cutaneous lymphomas exist and may be called for example as leukemic CTCL or CBCL, not-otherwise specified (NOS) leading to heterogeneous terminology between centers. Moreover, aggressive CL are rare occurring mainly in adults or elderly that limits therapeutic options and comparison of small groups in retrospective series. The distribution of diagnosis between the three main primary CBCL including marginal-zone lymphoma (MZL), CFCL and CLBCL, LT has considerably evolved and its heterogeneity between centers may also hamper uniform findings. Our proposal to classify large CBCL according to germinal center or non-germinal center origin has so far not been validated by others while in systemic lymphomas genomic profiling appears mandatory to identify patients with impaired prognosis. In the most frequent cutaneous lymphomas, no highly recurrent genetic mutation is commonly used for diagnosis purpose. Some genetic lesion such as CCND1 rearrangement in mantle cell lymphoma can serve a positive criteria of secondary skin involvement. Alternatively, exceptional primary anaplastic large cell lymphoma (ALCL) bear ALK rearrangement preventing to use such criteria as a hallmark of secondary skin ALCL. BCL2 rearrangement in primary CFCL contributes to identify patients at risk for extracutaneous spreading. Most reports found negative data for NAV3 rearrangement in CTCL that may not be a primary oncogenic driver but a secondary event. Interestingly, MYC rearrangement or double-hits may have a low impact on prognosis in CBCL while they are usually associated with impaired prognosis in systemic or nodal lymphomas. Alternatively, some highly recurrent mutation such as those of MYD88 in CLBCL, LT should be routinely assessed. While clinical presentation will remain a basis for CL diagnosis and treatment, it is now time to integrate molecular profiling in research studies or clinical trials to standardize diagnosis and to identify patients which will exhibit therapeutic resistance to conventional first-line treatment.