Soft tissue lymphoma

Abstract

Lymphoma can involve any part of the musculoskeletal system. Primary lymphoma has initially been described involving the skin, subcutaneous tissues (mycosis fungoides), muscles, synovium, nerve roots and bone. Secondary lymphomatous involvement of the musculoskeletal system is common, while primary malignant soft tissue lymphoma is rare and accounts for only 0.12% of soft tissue tumors [20, 29]. An increased incidence has been noted in recent years, possibly related to an increase in the number of immunocompromised patients [23]. Classification of malignant lymphoma continues to evolve from increased understanding of normal lymphoid cell differentiation as well as from observations on behavior and response to therapy within lymphoma subtypes. Therefore comparing studies and data should be made with precaution, respecting the fact that lymphomas have been classified by several systems over the past 30 years. The purpose of further classifying non-Hodgkins lymphomas into specific categories is to describe the individual behavior and to develop appropriate treatment strategies for each type of lymphoma. The most common classification system used in the 1980s-1990s was the International Working Formula- tion (IWF). The IWF divided non-Hodgkins lymphomas into three grades based on the microscopic appearance. This type of histological grading into low-grade, intermediate-grade and high-grade lymphoma is found throughout case reports and in the literature [26, 29]. Since the utilization of the IWF, additional work is done that further classifies non-Hodgkins lymphomas into individual cancers, each with specific features and behavior. This newer system is called the Revised European American Lymphoma (REAL) classification (1994). This REAL classification was so far updated in 1999 with the WHO modification [11] which recognizes three major categories of lymphoid malignancies based on morphology and cell lineage: B-cell neoplasms, Tcell/ natural killer (NK)-cell neoplasms, and Hodgkins lymphoma. Almost all cases described in the literature and reflected in our series are non-Hodgkins lymphomas, the majority of the B-cell type. Histological and immunophenotypic studies show a range of small lymphocytic, follicular, mixed, small noncleaved and large cell (anaplastic, immunoblastic and centroblastic) lymphoma. Only a minority of T- cell lymphoma of the soft tissues is reported in the literature [1, 6, 16, 18, 26]. A distinctive subtype of soft tissue lymphomas has been reported by Isaacson and Wright [13] in 1983 and named MALTomas, where MALT stands for mucosal associated lymphoid tissue. These are the extra-nodal equivalent of monocytoid (marginal zone) B-cell lymphomas occurring in lymphoid organs such as the lymph node. Although MALT lymphomas occur most frequently in the stomach, they have also been described in various nongastrointestinal sites, such as salivary gland, conjunctiva, thyroid, orbit, lung, breast, kidney, skin, liver, and prostate, as well as the central nervous system.Most of these organ systems lack native lymphoid tissue but acquire MALT in close association with chronic inflammation or autoimmune processes. MALT lymphomas appear to have similar clinical, pathological and molecular features regardless of the organ of origin. In the revised REAL-WHO classification, the MALT lymphomas were definitively classified among the marginal zone B-cell lymphomas.