In the current revised 4th edition of the World Health Organization (WHO) classification, ‘other iatrogenic immunodeficiency-associated lymphoproliferative disorders (Oii-LPDs)’ is listed in the last section in the chapter on immunodeficiency-associated lymphoproliferative disorders. Oii-LPDs cover a broad spectrum from benign lesions to lymphoma, and correspond to one of the subtypes in the WHO classification for immunocompetent patients.

The WHO classification does not clearly indicate the histological subtype of this disease category; however, the framework of subtype classification is similar to the classification of post-transplant lymphoproliferative disorders, and recent studies have attempted to subcategorize Oii-LPDs that fit this unique disease type. In this review, we provide an overview of B-cell-type Oii-LPDs regarding their histopathology and immunophenotype, genetics and clinical behaviors.

Other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPDs) with a T- or NK-cell phenotype are markedly rare, with only a limited number of cases having been reported thus far. Methotrexate (MTX) is the most common agent used for OIIA-LPD patients, and 43 cases of MTX-associated T-LPDs (MTX T-LPDs) and five cases of MTX-associated NK/T-LPDs (MTX NK-LPDs) have been described. In addition to MTX T-LPDs and MTX NK/T-LPDs, T-LPD and NK/T-LPDs have been reported in patients receiving other immunosuppressive agents such as thiopurines, TNF antagonists, and cyclosporine. Hepatosplenic T-cell lymphoma (HSTL) is specifically associated with iatrogenic immunodeficiency, and 10% of HSTL cases develop in patients receiving thiopurines and/or TNF antagonists for inflammatory bowel disease (IBD). In this review, we focused on MTX T-LPD, MTX NK/T-LPD, and HSTL in patients with IBD. These T- and NK/T-cell associated OIIA-LPDs are the most common in daily medical practice.

Epstein-Barr virus (EBV)-positive mucocutaneous ulcers (EBVMCUs) were first described as a lymphoproliferative disorder in 2010. Clinically, EBVMCUs are shallow, sharply circumscribed, unifocal mucosal or cutaneous ulcers that occur in immunosuppressed patients, including those with advanced age-associated immunosenescence, iatrogenic immunosuppression, primary immune disorders, and HIV/AIDS-associated immune deficiencies. In general, patients exhibit indolent disease progression and spontaneous regression. Histologically, EBVMCUs are characterized by the proliferation of EBV-positive, variable-sized, atypical B-cells. According to conventional histopathologic criteria, EBVMCUs may diagnosed as lymphomas. However, EBVMCUs are recognized as pseudomalignant lesions because they spontaneously regress without anti-cancer treatment. Therefore, overtreatment must be carefully avoided and multilateral differentiation is important. In this article, we reviewed previously reported EBVMCUs focusing on their clinical and pathological aspects in comparison with other EBV-positive B-cell neoplasms.

Other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPD), a category of immunodeficiency-associated LPD according to the World Health Organization classification, is associated with immunosuppressive drugs (ISDs). Several factors, including autoimmune disease (AID) activity, Epstein-Barr virus (EBV) infection, ISD usage, and aging, influence the development of OIIA-LPD, resulting in complicated clinical courses and outcomes. Most OIIA-LPD develops in patients with rheumatoid arthritis using methotrexate (MTX-LPD). The management of MTX-LPD is based on the clinical course, i.e., with/without regression, with/without relapse/regrowth event (RRE), LPD subtype, and ISDs for AIDs after LPD development. There are three clinical courses after ISD withdrawal: regressive LPD without relapse/regrowth (R-G), regressive LPD with RRE (R/R-G), and persistent LPD (P-G). The majority of EBV+ diffuse large B-cell lymphomas are classified in R-G, whereas classic Hodgkin lymphoma is generally classified in R/R-G. Polymorphic LPD (P-LPD) in MTX-LPD develops with heterogeneous pathological features similar to monomorphic LPD. Chemotherapy for MTX-LPD is selected according to that for de novo LPD, although the strategy for aggressive P-LPD and non-specific LPD is not well established. The absolute lymphocyte count in the peripheral blood has been suggested as a candidate marker for MTX-LPD development and RRE. Several clinical issues, including correct diagnosis among overlapping clinicopathological features in MTX-LPD and clinical management of LPD by ISDs other than MTX, require further investigation.