Abstract
Categorization of primary cutaneous B‐cell lymphomas (PCBCL) other than marginal zone (MZL) represents a diagnostic challenge with relevant prognostic implications. The 2008 WHO lymphoma classification recognizes only primary cutaneous follicular center cell lymphoma (PCFCCL) and primary cutaneous diffuse large B‐cell lymphoma, leg type (PCDLBCL‐LT), whereas the previous 2005 WHO/EORTC classification also included an intermediate form, namely PCDLBCL, other. We conducted a retrospective, multicentric, consensus‐based revision of the clinicopathologic characteristics of 161 cases of PCBCL other than MZL. Upon the histologic features that are listed in the WHO classification, 96 cases were classified as PCFCCL and 25 as PCDLBCL‐LT; 40 further cases did not fit in the former subgroups in terms of cytology and/or architecture, thus were classified as PCDLBCL, not otherwise specified (PCDLBCL‐NOS). We assigned all the cases a histogenetic profile, based on the immunohistochemical detection of CD10, BCL6, and MUM1, and a “double hit score” upon positivity for BCL2 and MYC. PCDLBCL‐NOS had a clinical presentation more similar to PCFCCL, whereas the histology was more consistent with the picture of a diffuse large B‐cell lymphoma, as predominantly composed of centroblasts but with intermixed a reactive infiltrate of small lymphocytes. Its behavior was intermediate between the other two forms, particularly when considering only cases with a “non‐germinal B‐cell” profile, whereas “germinal center” cases resembled PCFCCL. Our data confirmed the aggressive behavior of PCDLBC‐LT, which often coexpressed MYC and BCL2. The impact of single factors on 5‐year survival was documented, particularly histogenetic profile in PCDLBCL and BCL2 translocation in PCFCCL. Our study confirms that a further group—PCDLBCL‐NOS—exists, which can be recognized through a careful combination of histopathologic criteria coupled with adequate clinical information.
Highlights
The issue of classification of primary cutaneous B-cell lymphomas (PCBCL) other than marginal zone lymphoma (MZL) has been matter of debate
primary cutaneous follicular center cell lymphoma (PCFCCL) is defined on the basis of cytological features irrespective of growth pattern, which may be variable from follicular to predominantly diffuse; in some case, mostly advanced tumors, the lymphoma infiltrate may contain a prevalence of large cells, a feature which seems not to affect prognosis
PCDLBCL-L T designs all cutaneous B-c ell lymphomas with a diffuse pattern and composed of monotonous proliferation of centroblasts and immunoblasts, usually BCL2-positive, irrespective of site of presentation. This two-tiered distinction was validated by clinical studies [2, 3] and was partially supported by the identification of different molecular signatures and imbalances [4] in PCFCCL and PCDLBCL-L T, the latter resembling the activated B-cell type (ABC) of nodal DLBCL [5, 6]
Summary
The issue of classification of primary cutaneous B-cell lymphomas (PCBCL) other than marginal zone lymphoma (MZL) has been matter of debate. PCDLBCL-L T designs all cutaneous B-c ell lymphomas with a diffuse pattern and composed of monotonous proliferation of centroblasts and immunoblasts, usually BCL2-positive, irrespective of site of presentation. This two-tiered distinction was validated by clinical studies [2, 3] and was partially supported by the identification of different molecular signatures and imbalances [4] in PCFCCL and PCDLBCL-L T, the latter resembling the activated B-cell type (ABC) of nodal DLBCL [5, 6]. The present WHO lymphoma classification overcame the previous WHO/EORTC and included at least a part of PCDLBCL-O within the spectrum of PCFCCL
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