Review K E Y WORDS cutaneous lymphomas, T cell, B cell, classification, immuno- phenotyping, immuno- genotyping, review Cutaneous lymphomas Cutaneous lymphomns: update oj laboratory diagnosis. M. Alaibac, E. Tonin, A. Peserico, C. Veller-Fornasa SUMMARY The term primary cutaneous lymphomas designates a heterogeneous group of lymphoproliferative dis- orders arising from skin-homing T and B cells. The European Organization far Research and Treatment of Cancer (EORTC) classification far primary cutaneous lymphomas recognizes a limited number of cuta- neous T-cell lymphomas and cutaneous B-cell lymphomas and provides a working classification far cutaneous lymphomas. Herein, the diagnostic procedures far the diagnoses of cutaneous lymphomas are discussed. Recent developments regarding immunophenotyping and immunogenotyping of cutane- ous T-cell lymphomas and cutaneous B-cell lymphomas recognized in the EORTC classification are presented. The term primaiy cutaneous lymphomas designates a heterogeneous group of lymphoproliferative clisor- clers arising from skin-homing T and B cells which present in the skin with no evidence of extracutaneous disease at the tirne of diagnosis and six months thereaf- ter (1 -3). They are after the group of gastrointestinal lymphomas the second most common group of extra- nodal non-Hodgkin lymphomas with an annual inci- dence of 1-1.5/100,000. Classification. The European Organization for Research and Treat- ment of Cancer Classification (EORTC) uses a combi- nation of clinical, histological, immunophenotypic, ancl molecular biological characteristics and provides a working classification for cutaneous lymphomas (Table I) (4). The diagnosis of cutaneous lymphomas is macle by recognizing the clinical manifestations and is sup- ported by laborat01y tests. Immunophenotyping (im- munologic analysis of cellular antigen expression) ancl immunogenotyping (molecular biology analysis of an- tigen receptor genes) support the conventional clinical and histopathologic analyses. Immunophenotyping oj cutaneous lymphomas. · The clistinction between cutaneous lymphomas and non-lymphoid tumors of the skin is a common prob- lem. The most useful immunohistochemical marker in Acta Dermatoven APA Vol 10, 2001, No 2 - - ----------- ------------ - --- - ---- 47 Cutaneous lymplwmas this situation is the CD45 antibocly reacting with all the known isotypes of the CD45 family, also called the leu- kocyte common antigen family (LCA fam ily) . The anti- bocly labels the cell membrane of almost all leukocytes ancl is absent on non-haematopoietic cells (5). Mycosis fungoicles is a neoplasm of T helper lym- phocytes expressing the CD4 molecule and the pan-T- cell antigens CD2 ancl CD3 (1). They generally express the T-cell receptor molecules that consist of a ancl ~ chains (TCRa~) (6). Partial or complete loss of the T celi associatecl antigens CD5 and CD7 can sometimes be observed particularly among the intraepiclermal T cells and in the late stage of the disease (7, 8) . This ab- errant phenotype is considered circumstantial evidence of a neoplastic proliferation ofT-cells. A small percent- age of cases express CD8 rather than CD4. Benign re- active cutaneous diseases such as chronic eczema and psoriasis show the same pattern as that in early stage of mycos is fungoides (9). However cutaneous infiltrations in early mycosis fungoides contain significantly more CD4+ cells than those of benign lymphoid disorders. The CD4/CD8 ratio has been shown to be 4/1 in be- nign lymphoid infiltrates , 7 / 1 in the patch stage of my- cosis fungoides, 14/1 in the plaque stage of MF and 24/ 1 in the tumor stage (9). Patients may bave atypical lymphocytes w ith cere- briform nuclei (Sezary cells) in the peripheral blood. The current practice is to use a criterion of at least 20% cerebriform lymphocytes to define Sezary syndrome (10). Immunophenotypic studies ofthe peripheral bloocl may show expansion of a CD4+CD7- population re- fl ective of circulating atypical lymphocytes (10). Prima1y cutaneous large T-cell CD30+ lymphoma is the most common form on non-MF prima1y CTCL. The spectrum of primary cutaneous CD30+ lymphopro- liferative clisorders inclucles lymphomatoid papulosis , primary cutaneous large T-cell CD30+ lymphoma ancl intermediate forms (11). Lymphomatoid papulosis is characterized by scattered CD30+ blast cells whereas prima1y cutaneous large T-cell CD30+ lymphomas dem- onstrate cliffuse infiltrates of large anaplastic CD30+ T cells (11, 12). The CD30 molecule is expressed on the majority (>75%) of neoplastic cells. Most cases express the CD4+CD30+ phenotype with variable loss of pan-T celi antigens (CD2, CD3, CD5, or CD7) . A small minor- ity of cases is CD8+CD30+(12). Primaiy cutaneous large T-cell CD30- lymphomas are characterizecl by minimal or absent CD30 expres- sion (11 , 13). Tumor cells express a phenotype of the CD4+ lymphocyte subset. Occasional cases express CD8. Primary cutaneous pleomorphic small/medium- sized T-cell lymphomas are characterized by deep and 48 Table 1. EORTC classi/ication far primary cutaneous lymphomas. Indolent clinical behaviour Mycosis fungoides Mycosis fungoicles varianL~: follicular MF ancl pagetoicl reticulosis CTCL, large celi , CD30-positive (anaplastic, immunoblastic ancl large pleomorphic) Lymphomatoid papulosis Aggressive clinical behaviour Seza1y syndrome CTCL, large cel!, CD30-negative (immunoblastic and large pleomorphic) Provisional entities CTCL, pleomorphic, small/ medium-sized Subcutaneous panniculitis-like T-cell lymphoma ,, Indolent clinical behaviour Prima1y cutaneous immunocytoma/marginal zone B-cell lymphoma Prima1y cutaneous follicle center cell lymphoma Intermediate clinical behaviour Prima1y cutaneous large B-cell lymphoma of the leg Provisional entities Prima1y cutaneous plasmacytoma Intravascular large B-cell lymphoma diffuse infiltrates composed of small-to-medium sized atypical lymphoid cells expressing the CD4 molecule (11 , 14). CD8+ cutaneous pleomorphic lymphomas are rarely observed. A small minority expresses the y8 TCR and is characterizecl by an aggressive behavior. The loss of one or more pan-T antigens (CD2, CD3, CD5, or CD7) can be observecl . Primary cutaneous B-cell lymphomas are character- ized by a dense infiltrate of tumor cells expressing B- cell surface antigens, notably CD19, CD20, CD22 ancl CD79a (15, 16). Neoplastic cells may be Ig+ or Ig-. Ig+ B-cell lymphomas are monoclonal, ie, ali tumor cells express the same Ig light chain, either Kor 'A (1 5). This phenomenon is denominated light chain restriction. Reactive polyclonal B-cell infiltrates are composed of a mixture of K and 'A cells, tipically with approximately R ev i e w Acta Dermatoven APA Vol 10, 2001, No 2 Review 2.:1 K predominance. Therefare, the presence of light chain restriction is consistent with the presence of a CBCL. Immunogenotyping oj cutaneous lymphomas. The use of molecular biologic techniques has im- proved our ability to diagnose lymphocytic infiltrate of the skin and provided additional diagnostic parameters to complement clinical, histologic and immunophe- notipic analysis. Molecular characterization involves the identification of a monoclonal population of lympho- cytes which is based upon the detection of specific re- arrangements in the genes coding far antigen receptor in B-cells (Ig) and T-cells (the T-cell antigen receptor) (16,17). Southern blat analysis of genes coding far Igor far T-cell receptor was the method used in initial studies, which showed evidence far the monoclonal nature of both cutaneous T cell lymphoma (CTCL) and cutaneous B celi lymphoma (CBCL). More recently, Southern blat hybridization has been challenged by the polymerase chain reaction (PCR) far the routine analysis of clonality (18). Stuclies of clonality by means of PCR in patients with MF revealed elana! patterns in tumorous lesions, in erythrodermal stages, and in most infiltrated plaques, R ·1-,, ·1? ·1? ·1·) ·1;' ·N'