Cutaneous non hodgkin lymphomasC81-C96

Cutaneous lymphomas (CL) belong to the group of extranodal non-Hodgkin lymphomas (see below Non-Hodgkin lymphomas). They are defined as progressive, heterogeneous, malignant neoplasms of the lymphatic system of unknown etiology, originating from the skin or primarily affecting the skin.

• Primary cutaneous lymphomas, by definition, arise in the skin and usually remain confined to the skin organ for an extended period of time (at least 6 months).
• Secondary cutaneous l ymphomas arise from primary nodal or extranodal lymphomas in which the skin is affected as part of a disseminated infestation. This clear classification is not always unambiguous,

This distinction has fundamental diagnostic and therapeutic significance. It is not always possible to make this clear distinction.

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Primary cutaneous lymphomas encompass a broad, clinically and histologically heterogeneous spectrum of lymphoproliferative neoplasms, with approximately 70%-80% of cutaneous lymphomas being classified as cutaneous T-cell lymphomas, approximately 15-20% as cutaneous B-cell lymphomas, and +/-10% as other rare forms of cutaneous lymphomas. In principle, cutaneous lymphomas (CL) can be equated with "nodal" (originating from systemic lymphomas). However, the peculiarities of the skin-specific terrain (recirculation, homing phenomena, tropism of T lymphocytes for structures of the surface and adnexal epithelia) must be taken into account, which modify the specifications of the Kiel classification, which has existed since the seventies of the last century.

The EORTC classification and the current WHO classification describe nosological entities defined by clinical, histo- and cytomorphological as well as phenotypic and genotypic features. Since the EORTC classification better reflects the diversity and specificities of cutaneous lymphomas than the current WHO classification, it is recommended to use both classifications in parallel.

The "nodal" classifications of non-Hodgkin's lymphomas are in principle transferable to cutaneous lymphomas (CL) with regard to their basic subdivision into B- and T-cell lymphomas. Thus, all current classifications of cutaneous lymphomas follow this dualistic principle:

• Cutaneous T-cell lymphomas (CTCL) - about 70% of all cutaneous lymphomas.
• Primary cutaneous B-cell lymphomas (CBCL) - about 20% of all cutaneous lymphomas
• Neoplasms of unclear lineage assignment and differentiation (CD4+ CD65+hematoderma neoplasia - blastic NK-cell lymphoma)
• Other rare cutaneous lymphomas - about 10% of all cutaneous lymphomas

Classification according to prognostic and cytological/immunohistological criteria:

• Lymphomas with good prognosis (Indolent cutaneous lymphomas; median survival > 5 years).
• Lymphomas with moderate prognosis (median survival 2-5 years)
• Lymphomas with poor prognosis (aggressive cutaneous lymphomas; median survival < 2 years).

In contrast, the subdivisions of CTCL are less uniform. Thus, the present classifications essentially refer to low-malignant T-cell lymphoma of the mycosis fungoides type and some subspecificities, as well as its (generally clinically severe) erythrodermic leukemic variant, Sézary syndrome. Both syndromes are also recognized as entities in the different nodal classifications. This results in a frequency principle for cutaneous T-cell lymphomas (CTCL) according to general clinical aspects, which leads to the following (mental) subdivision:

• Cutaneous T-cell lymphomas of the mycosis fungoides type.
• Cutaneous T-cell lymphomas of the "non-mycosis fungoides" type.

Some lymphomas cannot be classified immunologically due to the absence of surface markers. Otherwise, in many cases, immunohistochemical and molecular biological methods (see CD classification) allow the correct phenotyping, classification and, in some cases, prognosis.

WHO-EORTC classification of cutaneous lymphomas Cutaneous T-cell and NK-cell lymphomas .

See below for classification.

• Cutaneous T-cell lymphomas
• Cutaneous B-cell lymphomas

Next to the gastrointestinal tract, the skin is the most common organ of manifestation of extranodal non-Hodgkin's lymphoma, with an incidence of 0.5-1.0/100,000 population/year.

In larger studies, mycosis fungoides is found most frequently (about 50% of all cutaneous lymphoma cases), followed by primary follicular lymphoma (16.9%) and lymphomatoid papulosis (15.9%).

CL low malignancy almost never occurs in patients <20 years of age. CL of high malignancy show 2 manifestation peaks: 5-15th LJ and 60-70th LJ. The average age at onset of the disease is >50 years, with the exception of patients with lymphomatoid papulosis. Patients with primary cutaneous diffuse large cell B-cell lymphoma have an average age of 80 years (Nashan D et al. 2018).

In cutaneous T-cell lymphomas, male patients predominate with about 75%. The mean age of onset of mycosis fungoides is 60 years (20-90 years).

Indolent BCL - m:w=1:1

Basically, unspecific and specific skin changes can be observed in lymphomas. Non-specific skin changes are hidden under eczematous, lichenoid or ichthyosiform, often pruriginous, exanthematic clinical pictures.

The cutaneous B-cell lymphomas appear rather monomorphic in their clinical and histological manifestation, characterized by mostly indolent, solitary but also disseminated, smooth, red to brown-red papules and nodules with nodular dermal and subcutaneous infiltrates with intact epidermis and mostly free border strip.

In contrast, the clinical and histological picture of cutaneous T-cell lymphomas is extremely varied and ranges from "ichthyosis-like" mucinosis follicularis, parapsoriasis en plaques with their extensive psoriasiform or eczematous plaques, to erythroderma. Ulcerated or non-ulcerated, small papular or large nodular lesions (0.5 cm to 15.0 cm) are also found. The lesions are solitary or disseminated, they tend to confluence. Not infrequently an arrangement aligned according to the cleavage lines of the skin is observed. This makes a clear clinical and histological classification extremely difficult and requires a lot of personal experience.

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