Lymphoproliferative lung disorders: clinicopathological aspects.

Lymphoproliferative disorders are rarely observed as primary lesions in the lung, representing only 0.3% of all primary pulmonary malignancies, ,1% of all the cases of non-Hodgkin lymphoma and 3–4% of all the extra nodal manifestations of non-Hodgkin lymphoma. The earliest comprehensive studies of pulmonary lymphomas were those of SALTZSTEIN [1] and PAPIOANNOU and WATSON [2], which were published in the 1960s. These investigators made important observations: low-grade neoplasms were more frequent than higher grade lymphomas (reticulum cell sarcomas) and both tumours had better clinical outcomes than their nodal-based counterparts. The authors also concluded that the majority of neoplasms with a low-grade cytological appearance should be considered as reactive proliferations, introducing the term ‘‘pseudolymphoma’’. This hypothesis showed significant weak points and, approximately 20 years later, ADDIS et al. [3] concluded that ‘‘most if not all the cases of pseudo-lymphoma can be classified, when re-evaluated, as malignant lymphoma’’. Knowledge of these entities expanded rapidly after the advent of new investigative tools such as immunohistochemistry and molecular biology techniques. The World Health Organization (WHO) classification of lymphoid neoplasm recently emphasised the importance of clinical features [4]. Table 1 provides an overall classification of lymphoproliferative disorders, which are described as: reactive/nonneoplastic lymphoid lesions, malignant parenchymal lymphoproliferative lesions (primary or secondary) and post-transplant lymphoproliferative disorders.