New insights and advances in defining primary cutaneous B-cell lymphomas and cutaneous B-cell-rich lymphoid proliferations

Primary cutaneous B-cell lymphomas (PCBCL) and lymphoid proliferations are a heterogenous group of entities arising primarily in the skin with a broad spectrum of clinical and histological characteristics. In general, the prognosis of these neoplasms is better than their systemic counterparts and this emphasizes the need for an accurate diagnosis for patients. Two main categories are recognized so far in PCBCL based on their clinical behaviour. Indolent PCBCL includes Primary cutaneous marginal zone lymphoma (PCMZL), Primary cutaneous follicle center lymphoma (PCFCL) and Epstein Barr virus-positive mucocutaneous ulcer (EBV + MCU). The more aggressive PCBCL are cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL, LT) and intravascular large B cell lymphoma. Since the publication of the updated WHO-EORTC classification in 2018, new consensus guidelines and classifications have been published in the field of cutaneous lymphomas incorporating new discoveries in their genetics alterations and immunophenotype. Here, we summarize the main clinical, histological and molecular characteristics of primary cutaneous B-cell lymphomas and reactive B-cell rich lymphoid proliferations, highlighting the most relevant findings published recently in the medical literature.